Chapter 5 Present Worth Analysis Lecture slides to accompany Engineering Economy 7th edition Leland Blank Anthony Tarquin 5-1 2012 by McGraw-Hill, New York, N.Y All Rights Reserved Formulating Alternatives Two types of economic proposals Mutually Exclusive (ME) Alternatives: Only one can be selected; Compete against each other Independent Projects: More than one can be selected; Compete only against DN Do Nothing (DN) An ME alternative or independent project to
maintain the current approach; no new costs, revenues or savings 5-2 2012 by McGraw-Hill All Rights Reserved Formulating Alternatives Two types of cash flow estimates Revenue: Alternatives include estimates of costs (cash outflows) and revenues (cash inflows) Cost: Alternatives include only costs; revenues and savings assumed equal for all alternatives; also called service alternatives 5-3 2012 by McGraw-Hill All Rights Reserved
PW Analysis of Alternatives Convert all cash flows to PW using MARR Precede costs by minus sign; receipts by plus sign EVALUATI ON> 0, it is justified For one project, if PW For mutually exclusive alternatives, select one with numerically largest PW For independent projects, select all with PW > 0 5-4 2012 by McGraw-Hill All Rights Reserved Selection of Alternatives by PW Project ID
Present Worth A B C D Solution: $30,000 $12,500 $-4,000 $ 2,000 (a) Select numerically largest PW; alternative A (b) Select all with PW > 0; projects A, B & D 5-5 2012 by McGraw-Hill All Rights Reserved
Example: PW Evaluation of Equal-Life ME Alts. Alternative X has a first cost of $20,000, an operating cost of $9,000 per year, and a $5,000 salvage value after 5 years. Alternative Y will cost $35,000 with an operating cost of $4,000 per year and a salvage value of $7,000 after 5 years. At an MARR of 12% per year, which should be selected? Solution: Find PW at MARR and select numerically larger PW value PWX = -20,000 - 9000(P/A,12%,5) + 5000(P/F,12%,5) = -$49,606 PWY = -35,000 - 4000(P/A,12%,5) + 7000(P/F,12%,5) = -$45,447 Select alternative Y 5-6 2012 by McGraw-Hill All Rights Reserved PW of Different-Life Alternatives Must compare alternatives for equal service (i.e., alternatives must end at the same time)
Two ways to compare equal service: Least common multiple (LCM) of lives Specified study period (The LCM procedure is used unless otherwise specified) 5-7 2012 by McGraw-Hill All Rights Reserved Assumptions of LCM approach Service provided is needed over the LCM or more years Selected alternative can be repeated over each life cycle of LCM in exactly the same manner Cash flow estimates are the same for each life cycle (i.e., change in exact accord with the inflation or deflation rate) 1-8
2012 by McGraw-Hill All Rights Reserved Example: Different-Life Alternatives Compare the machines below using present worth analysis at i = 10% per year First cost, $ Annual cost, $/year Salvage value, $ Life, years Solution: Machine A 20,000 9000 4000 3 Machine B 30,000
7000 6000 6 LCM = 6 years; repurchase A after 3 years PWA = -20,000 9000(P/A,10%,6) 16,000(P/F,10%,3) + 4000(P/F,10%,6) = $-68,961 PWB = -30,000 7000(P/A,10%,6) + 6000(P/F,10%,6) = $-57,100 20,000 4,000 in year 3 Select alternative B 5-9 2012 by McGraw-Hill All Rights Reserved
PW Evaluation Using a Study Period Once a study period is specified, all cash flows after this time are ignored Salvage value is the estimated market value at the end of study period Short study periods are often defined by management when business goals are short-term Study periods are commonly used in equipment replacement analysis 1-10 2012 by McGraw-Hill All Rights Reserved Example: Study Period PW Evaluation Compare the alternatives below using present worth analysis at i = 10% per year and a 3-year study period First cost, $ Annual cost, $/year Salvage/market value, $
Life, years Machine A -20,000 -9,000 4,000 3 Machine B -30,000 -7,000 6,000 (after 6 years) 10,000 (after 3 years) 6 Solution: Study period = 3 years; disregard all estimates after 3 years PWA = -20,000 9000(P/A,10%,3) + 4000(P/F,10%,3) = $-39,376 PWB = -30,000 7000(P/A,10%,3) + 10,000(P/F,10%,3)= $-39,895 Marginally, select A; different selection than for LCM = 6 years 5-11
2012 by McGraw-Hill All Rights Reserved Future Worth Analysis FW exactly like PW analysis, except calculate FW Must compare alternatives for equal service (i.e. alternatives must end at the same time) Two ways to compare equal service: Least common multiple (LCM) of lives Specified study period (The LCM procedure is used unless otherwise specified) 5-12 2012 by McGraw-Hill All Rights Reserved
FW of Different-Life Alternatives Compare the machines below using future worth analysis at i = 10% per year First cost, $ Annual cost, $/year Salvage value, $ Life, years Solution: Machine B -30,000 -7000 6000 6 Machine A -20,000 -9000 4000 3
LCM = 6 years; repurchase A after 3 years FWA = -20,000(F/P,10%,6) 9000(F/A,10%,6) 16,000(F/P,10%,3) + 4000 = $-122,168 FWB = -30,000(F/P,10%.6) 7000(F/A,10%,6) + 6000 = $-101,157 Select B (Note: PW and FW methods will always result in same selection) 5-13 2012 by McGraw-Hill All Rights Reserved Capitalized Cost (CC) Analysis CC refers to the present worth of a project with a very long life, that is, PW as n becomes infinite Basic equation is: CC = P = A i A essentially represents the interest on a perpetual investment For example, in order to be able to withdraw $50,000 per year forever at i = 10% per year, the amount of capital required is 50,000/0.10 = $500,000
For finite life alternatives, convert all cash flows into an A value over one life cycle and then divide by i 5-14 2012 by McGraw-Hill All Rights Reserved Example: Capitalized Cost Compare the machines shown below on the basis of their capitalized cost. Use i = 10% per year Machine 1 Machine 2 First cost,$ -20,000 -100,000 Annual cost,$/year -9000 -7000 Salvage value, $
----4000 Life, years 3 Solution: Convert machine 1 cash flows into A and then divide by i A1 = -20,000(A/P,10%,3) 9000 + 4000(A/F,10%,3) = $-15,834 CC1 = -15,834 / 0.10 = $-158,340 CC2 = -100,000 7000/ 0.10 = $-170,000 Select machine 1 5-15 2012 by McGraw-Hill All Rights Reserved Summary of Important Points PW method converts all cash flows to present value at MARR Alternatives can be mutually exclusive or independent Cash flow estimates can be for revenue or cost alternatives PW comparison must always be made for equal service
Equal service is achieved by using LCM or study period Capitalized cost is PW of project with infinite life; CC = P = A/i 5-16 2012 by McGraw-Hill All Rights Reserved
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