# Present value

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In economics and finance, present value (PV), also known as present discounted value, is the value of an expected income stream determined as of the date of valuation. The present value is always less than or equal to the future value because money has interest-earning potential, a characteristic referred to as the time value of money, except during times of negative interest rates, when the present value will be more than the future value. [1] Time value can be described with the simplified phrase, "A dollar today is worth more than a dollar tomorrow". Here, 'worth more' means that its value is greater. A dollar today is worth more than a dollar tomorrow because the dollar can be invested and earn a day's worth of interest, making the total accumulate to a value more than a dollar by tomorrow. Interest can be compared to rent. [2] Just as rent is paid to a landlord by a tenant without the ownership of the asset being transferred, interest is paid to a lender by a borrower who gains access to the money for a time before paying it back. By letting the borrower have access to the money, the lender has sacrificed the exchange value of this money, and is compensated for it in the form of interest. The initial amount of the borrowed funds (the present value) is less than the total amount of money paid to the lender.

Economics is the social science that studies the production, distribution, and consumption of goods and services.

Finance is a field that is concerned with the allocation (investment) of assets and liabilities over space and time, often under conditions of risk or uncertainty. Finance can also be defined as the art of money management. Participants in the market aim to price assets based on their risk level, fundamental value, and their expected rate of return. Finance can be split into three sub-categories: public finance, corporate finance and personal finance.

Interest, in finance and economics, is payment from a borrower or deposit-taking financial institution to a lender or depositor of an amount above repayment of the principal sum, at a particular rate. It is distinct from a fee which the borrower may pay the lender or some third party. It is also distinct from dividend which is paid by a company to its shareholders (owners) from its profit or reserve, but not at a particular rate decided beforehand, rather on a pro rata basis as a share in the reward gained by risk taking entrepreneurs when the revenue earned exceeds the total costs.

## Contents

Present value calculations, and similarly future value calculations, are used to value loans, mortgages, annuities, sinking funds, perpetuities, bonds, and more. These calculations are used to make comparisons between cash flows that don’t occur at simultaneous times, [1] since time dates must be consistent in order to make comparisons between values. When deciding between projects in which to invest, the choice can be made by comparing respective present values of such projects by means of discounting the expected income streams at the corresponding project interest rate, or rate of return. The project with the highest present value, i.e. that is most valuable today, should be chosen.

Future value is the value of an asset at a specific date. It measures the nominal future sum of money that a given sum of money is "worth" at a specified time in the future assuming a certain interest rate, or more generally, rate of return; it is the present value multiplied by the accumulation function. The value does not include corrections for inflation or other factors that affect the true value of money in the future. This is used in time value of money calculations.

A sinking fund is a fund established by an economic entity by setting aside revenue over a period of time to fund a future capital expense, or repayment of a long-term debt.

In finance, a bond is an instrument of indebtedness of the bond issuer to the holders. The most common types of bonds include municipal bonds and corporate bonds.

The traditional method of valuing future income streams as a present capital sum is to multiply the average expected annual cash-flow by a multiple, known as "years' purchase". For example, in selling to a third party a property leased to a tenant under a 99-year lease at a rent of $10,000 per annum, a deal might be struck at "20 years' purchase", which would value the lease at 20 *$10,000, i.e. $200,000. This equates to a present value discounted in perpetuity at 5%. For a riskier investment the purchaser would demand to pay a lower number of years' purchase. This was the method used for example by the English crown in setting re-sale prices for manors seized at the Dissolution of the Monasteries in the early 16th century. The standard usage was 20 years' purchase. [3] The Dissolution of the Monasteries, sometimes referred to as the Suppression of the Monasteries, was the set of administrative and legal processes between 1536 and 1541 by which Henry VIII disbanded monasteries, priories, convents and friaries in England, Wales and Ireland, appropriated their income, disposed of their assets, and provided for their former personnel and functions. Although the policy was originally envisaged as increasing the regular income of the Crown, much former monastic property was sold off to fund Henry's military campaigns in the 1540s. He was given the authority to do this in England and Wales by the Act of Supremacy, passed by Parliament in 1534, which made him Supreme Head of the Church in England, thus separating England from Papal authority, and by the First Suppression Act (1535) and the Second Suppression Act (1539). ## Background If offered a choice between$100 today or $100 in one year, and there is a positive real interest rate throughout the year, ceteris paribus , a rational person will choose$100 today. This is described by economists as time preference. Time preference can be measured by auctioning off a risk free security—like a US Treasury bill. If a $100 note with a zero coupon, payable in one year, sells for$80 now, then $80 is the present value of the note that will be worth$100 a year from now. This is because money can be put in a bank account or any other (safe) investment that will return interest in the future.

Ceteris paribus or caeteris paribus is a Latin phrase meaning "other things equal"; English translations of the phrase include "all other things being equal" or "other things held constant" or "all else unchanged"; A prediction or a statement about a causal, empirical, or logical relation between two states of affairs is ceteris paribus if it is acknowledged that the prediction, although usually accurate in expected conditions, can fail or the relation can be abolished by intervening factors.

In economics, time preference is the current relative valuation placed on receiving a good at an earlier date compared with receiving it at a later date.

An investor who has some money has two options: to spend it right now or to save it. But the financial compensation for saving it (and not spending it) is that the money value will accrue through the compound interest that he or she will receive from a borrower (the bank account in which he has the money deposited).

Compound interest is the addition of interest to the principal sum of a loan or deposit, or in other words, interest on interest. It is the result of reinvesting interest, rather than paying it out, so that interest in the next period is then earned on the principal sum plus previously accumulated interest. Compound interest is standard in finance and economics.

Therefore, to evaluate the real value of an amount of money today after a given period of time, economic agents compound the amount of money at a given (interest) rate. Most actuarial calculations use the risk-free interest rate which corresponds to the minimum guaranteed rate provided by a bank's saving account for example, assuming no risk of default by the bank to return the money to the account holder on time. To compare the change in purchasing power, the real interest rate (nominal interest rate minus inflation rate) should be used.

The risk-free interest rate is the rate of return of a hypothetical investment with no risk of financial loss, over a given period of time.

The real interest rate is the rate of interest an investor, saver or lender receives after allowing for inflation. It can be described more formally by the Fisher equation, which states that the real interest rate is approximately the nominal interest rate minus the inflation rate.

In finance and economics, the nominal interest rate or nominal rate of interest is either of two distinct things:

1. the rate of interest before adjustment for inflation ; or,
2. for interest rates "as stated" without adjustment for the full effect of compounding. An interest rate is called nominal if the frequency of compounding is not identical to the basic time unit in which the nominal rate is quoted.

The operation of evaluating a present value into the future value is called a capitalization (how much will $100 today be worth in 5 years?). The reverse operation—evaluating the present value of a future amount of money—is called a discounting (how much will$100 received in 5 years—at a lottery for example—be worth today?).

It follows that if one has to choose between receiving $100 today and$100 in one year, the rational decision is to choose the $100 today. If the money is to be received in one year and assuming the savings account interest rate is 5%, the person has to be offered at least$105 in one year so that the two options are equivalent (either receiving $100 today or receiving$105 in one year). This is because if $100 is deposited in a savings account, the value will be$105 after one year, again assuming no risk of losing the initial amount through bank default.

## Interest rates

Interest is the additional amount of money gained between the beginning and the end of a time period. Interest represents the time value of money, and can be thought of as rent that is required of a borrower in order to use money from a lender. [2] [4] For example, when an individual takes out a bank loan, the individual is charged interest. Alternatively, when an individual deposits money into a bank, the money earns interest. In this case, the bank is the borrower of the funds and is responsible for crediting interest to the account holder. Similarly, when an individual invests in a company (through corporate bonds, or through stock), the company is borrowing funds, and must pay interest to the individual (in the form of coupon payments, dividends, or stock price appreciation). [1] The interest rate is the change, expressed as a percentage, in the amount of money during one compounding period. A compounding period is the length of time that must transpire before interest is credited, or added to the total. [2] For example, interest that is compounded annually is credited once a year, and the compounding period is one year. Interest that is compounded quarterly is credited four times a year, and the compounding period is three months. A compounding period can be any length of time, but some common periods are annually, semiannually, quarterly, monthly, daily, and even continuously.

There are several types and terms associated with interest rates:

## Calculation

The operation of evaluating a present sum of money some time in the future is called a capitalization (how much will 100 today be worth in five years?). The reverse operation—evaluating the present value of a future amount of money—is called discounting (how much will 100 received in five years be worth today?). [4]

Spreadsheets commonly offer functions to compute present value. In Microsoft Excel, there are present value functions for single payments - "=NPV(...)", and series of equal, periodic payments - "=PV(...)". Programs will calculate present value flexibly for any cash flow and interest rate, or for a schedule of different interest rates at different times.

### Present value of a lump sum

The most commonly applied model of present valuation uses compound interest. The standard formula is:

${\displaystyle PV={\frac {C}{(1+i)^{n}}}\,}$

Where ${\displaystyle \,C\,}$ is the future amount of money that must be discounted, ${\displaystyle \,n\,}$ is the number of compounding periods between the present date and the date where the sum is worth ${\displaystyle \,C\,}$, ${\displaystyle \,i\,}$ is the interest rate for one compounding period (the end of a compounding period is when interest is applied, for example, annually, semiannually, quarterly, monthly, daily). The interest rate, ${\displaystyle \,i\,}$, is given as a percentage, but expressed as a decimal in this formula.

Often, ${\displaystyle v^{n}=\,(1+i)^{-n}}$ is referred to as the Present Value Factor [2]

This is also found from the formula for the future value with negative time.

For example, if you are to receive $1000 in five years, and the effective annual interest rate during this period is 10% (or 0.10), then the present value of this amount is ${\displaystyle PV={\frac {\1000}{(1+0.10)^{5}}}=\620.92\,}$ The interpretation is that for an effective annual interest rate of 10%, an individual would be indifferent to receiving$1000 in five years, or $620.92 today. [1] The purchasing power in today's money of an amount ${\displaystyle \,C\,}$ of money, ${\displaystyle \,n\,}$ years into the future, can be computed with the same formula, where in this case ${\displaystyle \,i\,}$ is an assumed future inflation rate. ### Net present value of a stream of cash flows A cash flow is an amount of money that is either paid out or received, differentiated by a negative or positive sign, at the end of a period. Conventionally, cash flows that are received are denoted with a positive sign (total cash has increased) and cash flows that are paid out are denoted with a negative sign (total cash has decreased). The cash flow for a period represents the net change in money of that period. [4] Calculating the net present value, ${\displaystyle \,NPV\,}$, of a stream of cash flows consists of discounting each cash flow to the present, using the present value factor and the appropriate number of compounding periods, and combining these values. [1] For example, if a stream of cash flows consists of +$100 at the end of period one, -$50 at the end of period two, and +$35 at the end of period three, and the interest rate per compounding period is 5% (0.05) then the present value of these three Cash Flows are:

${\displaystyle PV_{1}={\frac {\100}{(1.05)^{1}}}=\95.24\,}$
${\displaystyle PV_{2}={\frac {-\50}{(1.05)^{2}}}=-\45.35\,}$
${\displaystyle PV_{3}={\frac {\35}{(1.05)^{3}}}=\30.23\,}$ respectively

Thus the net present value would be:

${\displaystyle NPV=PV_{1}+PV_{2}+PV_{3}={\frac {100}{(1.05)^{1}}}+{\frac {-50}{(1.05)^{2}}}+{\frac {35}{(1.05)^{3}}}=95.24-45.35+30.23=80.12,}$

There are a few considerations to be made.

• The periods might not be consecutive. If this is the case, the exponents will change to reflect the appropriate number of periods
• The interest rates per period might not be the same. The cash flow must be discounted using the interest rate for the appropriate period: if the interest rate changes, the sum must be discounted to the period where the change occurs using the second interest rate, then discounted back to the present using the first interest rate. [2] For example, if the cash flow for period one is $100, and$200 for period two, and the interest rate for the first period is 5%, and 10% for the second, then the net present value would be:
${\displaystyle NPV=100\,(1.05)^{-1}+200\,(1.10)^{-1}\,(1.05)^{-1}={\frac {100}{(1.05)^{1}}}+{\frac {200}{(1.10)^{1}(1.05)^{1}}}=\95.24+\173.16=\268.40}$
• The interest rate must necessarily coincide with the payment period. If not, either the payment period or the interest rate must be modified. For example, if the interest rate given is the effective annual interest rate, but cash flows are received (and/or paid) quarterly, the interest rate per quarter must be computed. This can be done by converting effective annual interest rate, ${\displaystyle \,i\,}$, to nominal annual interest rate compounded quarterly:
${\displaystyle (1+i)=\left(1+{\frac {i^{4}}{4}}\right)^{4}}$ [2]

Here, ${\displaystyle i^{4}}$ is the nominal annual interest rate, compounded quarterly, and the interest rate per quarter is ${\displaystyle {\frac {i^{4}}{4}}}$

#### Present value of an annuity

Many financial arrangements (including bonds, other loans, leases, salaries, membership dues, annuities including annuity-immediate and annuity-due, straight-line depreciation charges) stipulate structured payment schedules; payments of the same amount at regular time intervals. Such an arrangement is called an annuity. The expressions for the present value of such payments are summations of geometric series.

There are two types of annuities: an annuity-immediate and annuity-due. For an annuity immediate, ${\displaystyle \,n\,}$ payments are received (or paid) at the end of each period, at times 1 through ${\displaystyle \,n\,}$, while for an annuity due, ${\displaystyle \,n\,}$ payments are received (or paid) at the beginning of each period, at times 0 through ${\displaystyle \,n-1\,}$. [4] This subtle difference must be accounted for when calculating the present value.

An annuity due is an annuity immediate with one more interest-earning period. Thus, the two present values differ by a factor of ${\displaystyle (1+i)}$:

${\displaystyle PV_{\text{annuity due}}=PV_{\text{annuity immediate}}(1+i)\,\!}$ [2]

The present value of an annuity immediate is the value at time 0 of the stream of cash flows:

${\displaystyle PV=\sum _{k=1}^{n}{\frac {C}{(1+i)^{k}}}=C\left[{\frac {1-(1+i)^{-n}}{i}}\right],\qquad (1)}$

where:

${\displaystyle \,n\,}$ = number of periods,
${\displaystyle \,C\,}$ = amount of cash flows,
${\displaystyle \,i\,}$ = effective periodic interest rate or rate of return.

#### An approximation for annuity and loan calculations

The above formula (1) for annuity immediate calculations offers little insight for the average user and requires the use of some form of computing machinery. There is an approximation which is less intimidating, easier to compute and offers some insight for the non-specialist. It is given by [5]

${\displaystyle C\approx PV\left({\frac {1}{n}}+{\frac {2}{3}}i\right)}$

Where, as above, C is annuity payment, PV is principal, n is number of payments, starting at end of first period, and i is interest rate per period. Equivalently C is the periodic loan repayment for a loan of PV extending over n periods at interest rate, i. The formula is valid (for positive n, i) for ni≤3. For completeness, for ni≥3 the approximation is ${\displaystyle C\approx PVi}$.

The formula can, under some circumstances, reduce the calculation to one of mental arithmetic alone. For example, what are the (approximate) loan repayments for a loan of PV = $10,000 repaid annually for n = ten years at 15% interest (i = 0.15)? The applicable approximate formula is C ≈ 10,000*(1/10 + (2/3) 0.15) = 10,000*(0.1+0.1) = 10,000*0.2 =$2000 pa by mental arithmetic alone. The true answer is \$1993, very close.

The overall approximation is accurate to within ±6% (for all n≥1) for interest rates 0≤i≤0.20 and within ±10% for interest rates 0.20≤i≤0.40. It is, however, intended only for "rough" calculations.

#### Present value of a perpetuity

A perpetuity refers to periodic payments, receivable indefinitely, although few such instruments exist. The present value of a perpetuity can be calculated by taking the limit of the above formula as n approaches infinity.

${\displaystyle PV\,=\,{\frac {C}{i}}.\qquad (2)}$

Formula (2) can also be found by subtracting from (1) the present value of a perpetuity delayed n periods, or directly by summing the present value of the payments

${\displaystyle PV=\sum _{k=1}^{\infty }{\frac {C}{(1+i)^{k}}}={\frac {C}{i}},\qquad i>0,}$

which form a geometric series.

Again there is a distinction between a perpetuity immediate – when payments received at the end of the period – and a perpetuity due – payment received at the beginning of a period. And similarly to annuity calculations, a perpetuity due and a perpetuity immediate differ by a factor of ${\displaystyle (1+i)}$:

${\displaystyle PV_{\text{perpetuity due}}=PV_{\text{perpetuity immediate}}(1+i)\,\!}$ [2]

#### PV of a bond

A corporation issues a bond, an interest earning debt security, to an investor to raise funds. [4] The bond has a face value, ${\displaystyle F}$, coupon rate, ${\displaystyle r}$, and maturity date which in turn yields the number of periods until the debt matures and must be repaid. A bondholder will receive coupon payments semiannually (unless otherwise specified) in the amount of ${\displaystyle Fr}$, until the bond matures, at which point the bondholder will receive the final coupon payment and the face value of a bond, ${\displaystyle F(1+r)}$. The present value of a bond is the purchase price. [2] The purchase price is equal to the bond's face value if the coupon rate is equal to the current interest rate of the market, and in this case, the bond is said to be sold 'at par'. If the coupon rate is less than the market interest rate, the purchase price will be less than the bond's face value, and the bond is said to have been sold 'at a discount', or below par. Finally, if the coupon rate is greater than the market interest rate, the purchase price will be greater than the bond's face value, and the bond is said to have been sold 'at a premium', or above par. [4] The purchase price can be computed as:

${\displaystyle PV=\left[\sum _{k=1}^{n}Fr(1+i)^{-k}\right]}$${\displaystyle +F(1+i)^{-n}}$

#### Technical details

Present value is additive. The present value of a bundle of cash flows is the sum of each one's present value.

In fact, the present value of a cashflow at a constant interest rate is mathematically one point in the Laplace transform of that cashflow, evaluated with the transform variable (usually denoted "s") equal to the interest rate. The full Laplace transform is the curve of all present values, plotted as a function of interest rate. For discrete time, where payments are separated by large time periods, the transform reduces to a sum, but when payments are ongoing on an almost continual basis, the mathematics of continuous functions can be used as an approximation.

These calculations must be applied carefully, as there are underlying assumptions:

• That it is not necessary to account for price inflation, or alternatively, that the cost of inflation is incorporated into the interest rate.
• That the likelihood of receiving the payments is high—or, alternatively, that the default risk is incorporated into the interest rate.

See time value of money for further discussion.

### Variants/approaches

There are mainly two flavors of Present Value. Whenever there will be uncertainties in both timing and amount of the cash flows, the expected present value approach will often be the appropriate technique.

• Traditional Present Value Approach – in this approach a single set of estimated cash flows and a single interest rate (commensurate with the risk, typically a weighted average of cost components) will be used to estimate the fair value.
• Expected Present Value Approach – in this approach multiple cash flows scenarios with different/expected probabilities and a credit-adjusted risk free rate are used to estimate the fair value.

### Choice of interest rate

The interest rate used is the risk-free interest rate if there are no risks involved in the project. The rate of return from the project must equal or exceed this rate of return or it would be better to invest the capital in these risk free assets. If there are risks involved in an investment this can be reflected through the use of a risk premium. The risk premium required can be found by comparing the project with the rate of return required from other projects with similar risks. Thus it is possible for investors to take account of any uncertainty involved in various investments.

## Present value method of valuation

An investor, the lender of money, must decide the financial project in which to invest their money, and present value offers one method of deciding. [1] A financial project requires an initial outlay of money, such as the price of stock or the price of a corporate bond. The project claims to return the initial outlay, as well as some surplus (for example, interest, or future cash flows). An investor can decide which project to invest in by calculating each projects’ present value (using the same interest rate for each calculation) and then comparing them. The project with the smallest present value – the least initial outlay – will be chosen because it offers the same return as the other projects for the least amount of money. [2]

## Related Research Articles

In finance, discounted cash flow (DCF) analysis is a method of valuing a project, company, or asset using the concepts of the time value of money. All future cash flows are estimated and discounted by using cost of capital to give their present values (PVs). The sum of all future cash flows, both incoming and outgoing, is the net present value (NPV), which is taken as the value of the cash flows in question.

Discounting is a financial mechanism in which a debtor obtains the right to delay payments to a creditor, for a defined period of time, in exchange for a charge or fee. Essentially, the party that owes money in the present purchases the right to delay the payment until some future date. The discount, or charge, is the difference between the original amount owed in the present and the amount that has to be paid in the future to settle the debt.

In finance, the net present value (NPV) or net present worth (NPW) applies to a series of cash flows occurring at different times. The present value of a cash flow depends on the interval of time between now and the cash flow. It also depends on the discount rate. NPV accounts for the time value of money. It provides a method for evaluating and comparing capital projects or financial products with cash flows spread over time, as in loans, investments, payouts from insurance contracts plus many other applications.

The internal rate of return (IRR) is a measure of an investment’s rate of return. The term internal refers to the fact that the calculation excludes external factors, such as the risk-free rate, inflation, the cost of capital, or various financial risks.

The time value of money is the greater benefit of receiving money now rather than an identical sum later. It is founded on time preference.

In finance, an interest rate swap (IRS) is an interest rate derivative (IRD). It involves exchange of interest rates between two parties. In particular it is a linear IRD and one of the most liquid, benchmark products. It has associations with forward rate agreements (FRAs), and with zero coupon swaps (ZCSs).

A perpetuity is an annuity that has no end, or a stream of cash payments that continues forever. There are few actual perpetuities in existence. For example, the United Kingdom (UK) government issued them in the past; these were known as consols and were all finally redeemed in 2015. Real estate and preferred stock are among some types of investments that effect the results of a perpetuity, and prices can be established using techniques for valuing a perpetuity. Perpetuities are but one of the time value of money methods for valuing financial assets. Perpetuities are a form of ordinary annuities.

Rational pricing is the assumption in financial economics that asset prices will reflect the arbitrage-free price of the asset as any deviation from this price will be "arbitraged away". This assumption is useful in pricing fixed income securities, particularly bonds, and is fundamental to the pricing of derivative instruments.

Bond valuation is the determination of the fair price of a bond. As with any security or capital investment, the theoretical fair value of a bond is the present value of the stream of cash flows it is expected to generate. Hence, the value of a bond is obtained by discounting the bond's expected cash flows to the present using an appropriate discount rate.

In finance, the duration of a financial asset that consists of fixed cash flows, for example a bond, is the weighted average of the times until those fixed cash flows are received. When the price of an asset is considered as a function of yield, duration also measures the price sensitivity to yield, the rate of change of price with respect to yield or the percentage change in price for a parallel shift in yields.

Actuarial notation is a shorthand method to allow actuaries to record mathematical formulas that deal with interest rates and life tables.

In finance, return is a profit on an investment. It comprises any change in value of the investment, and/or cash flows which the investor receives from the investment, such as interest payments or dividends. It may be measured either in absolute terms or as a percentage of the amount invested. The latter is also called the holding period return.

Mortgage calculators are automated tools that enable users to determine the financial implications of changes in one or more variables in a mortgage financing arrangement. Mortgage calculators are used by consumers to determine monthly repayments, and by mortgage providers to determine the financial suitability of a home loan applicant.

In finance, mortgage yield is a measure of yield of mortgage-backed bonds. It is also known as cash flow yield. The mortgage yield, or cash flow yield, of a mortgage-backed bond is the monthly compounded discount rate at which net present value of all future cash flows from the bond will be equal to the present price of the bond.

In finance, the weighted-average life (WAL) of an amortizing loan or amortizing bond, also called average life, is the weighted average of the times of the principal repayments: it's the average time until a dollar of principal is repaid.

Analogous to continuous compounding, a continuous annuity is an ordinary annuity in which the payment interval is narrowed indefinitely. A (theoretical) continuous repayment mortgage is a mortgage loan paid by means of a continuous annuity.

An annuity is a series of payments made at equal intervals. Examples of annuities are regular deposits to a savings account, monthly home mortgage payments, monthly insurance payments and pension payments. Annuities can be classified by the frequency of payment dates. The payments (deposits) may be made weekly, monthly, quarterly, yearly, or at any other regular interval of time.

In finance, a zero coupon swap (ZCS) is an interest rate derivative (IRD). In particular it is a linear IRD, that in its specification is very similar to the much more widely traded interest rate swap (IRS).

## References

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2. Broverman, Samuel (2010). Mathematics of Investment and Credit. Winsted: ACTEX Publishers. pp. 4–229. ISBN   9781566987677.
3. Youings, Joyce, "Devon Monastic Lands: Calendar of Particulars for Grants 1536–1558", Devon & Cornwall Record Society, New Series, Vol.1, 1955
4. Ross, Stephen; Randolph W. Westerfield; Bradford D. Jordan (2010). Fundamentals of Corporate Finance (9 ed.). New York: McGraw-Hill. pp. 145–287. ISBN   9780077246129.
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