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Lecture 5: Inflation: Engineering Economy

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Lecture 5 : Inflation

Lecture slides to accompany

Engineering Economy
7th edition

Leland Blank
Anthony Tarquin
LEARNING OUTCOMES

• Relationship between Inflation and Purchasing Power

• Constant Value Dollar and Purchasing Power

• 3 Different Ways of Stating an Interest Rate


• Calculate PW, FW and AW of cashflows with inflation
considered.
Understanding Inflation
Inflation: Increase in amount of money needed to purchase same amount
of goods or services. Inflation results in a decrease in purchasing power,
i.e., one unit of money buys less goods or services

• Purchasing power is a good indicator for the real value of money (real
money)
• Increase in money supply (related very much with the interest rate dictated by
the central bank) - As the value of money decreases (because of its
abundancy), it takes more money for the same amount of goods or services.
• Reduce or stagnant productivity i.e. constant amount of money, less goods
Constant Value Dollar
The money that maintain its value over time i.e represents the same
purchasing power over time.
Constant Value (Real Dollar) Actual Dollar
Year RM
0 RM 100 RM 100
1 RM 100 RM 100 (1+0.05)
2 RM 100 RM 100 (1+0.05)2

Say we have an inflation of 5% Give more to compensate for the


inflation (decrease value of
money)
Constant Value Dollar Definition
An adjusted value of currency used to compare dollar values from one
period to another. Due to inflation, the purchasing power of the dollar
changes over time, so in order to compare dollar values from one year to
another, they need to be converted from nominal (current) dollar values to
constant dollar values.

Constant dollar value may also be referred to as real dollar or today’s


dollar (present dollar).
Money Time Value due to the Inflation

Money in one period of time t1, can be brought to the same value as
money in another period of time t2 by using;

𝑎𝑚𝑜𝑢𝑛𝑡 𝑖𝑛 𝑝𝑒𝑟𝑖𝑜𝑑 𝑡2
𝐴𝑚𝑜𝑢𝑛𝑡 𝑖𝑛 𝑝𝑒𝑟𝑖𝑜𝑑 𝑡1 = (𝐄𝐪. 𝟏)
𝑖𝑛𝑓𝑙𝑎𝑡𝑖𝑜𝑛 𝑟𝑎𝑡𝑒 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 𝑡1 𝑎𝑛𝑑 𝑡2

Lets use dollar as the currency.


Dollars in period t1are called constant value dollar (present dollar).
Dollars in period t2 are called future dollars which have taken
inflation into account.
If f is the inflation rate per period, and t is the number of period between
time t1 and t2.

Equation (Eq. 1) can be rewrite as;

𝐹𝑢𝑡𝑢𝑟𝑒 𝐷𝑜𝑙𝑙𝑎𝑟𝑠
𝐶𝑜𝑛𝑠𝑡𝑎𝑛𝑡 𝑉𝑎𝑙𝑢𝑒 𝐷𝑜𝑙𝑙𝑎𝑟𝑠 = 𝑡
(𝐄𝐪. 𝟐)
(1 + 𝑓)

𝐹𝑢𝑡𝑢𝑟𝑒 𝐷𝑜𝑙𝑙𝑎𝑟𝑠 = Constant Value Dollars (1 + 𝑓)𝑡 (𝐄𝐪. 𝟑)

𝑭𝑽 = 𝑷𝑽(𝟏 + 𝒓)𝒕
Three Different Interest Rates
► Real accumulation of wealth or interest rate i – Rate at which
interest is earned when effects of inflation are removed; i represents
the real increase in purchasing power

►Inflation rate f – Rate of change in value of currency

►Market or inflation-adjusted rate if – Rate that takes inflation into


account. Commonly stated rate everyday

if = i + f + (i)(f) Please memorize this equation


Example: Constant Value Dollars
How much would be required today to purchase an item that increased in cost
by exactly the inflation rate? The cost 30 years ago was $1000 and inflation has
consistently averaged 4% per year.
Solution: Solve for future dollars

Future dollars = constant value dollars(1 + f)t


= 1000(1 + 0.04)30
= $3243

Note: This calculation only accounts for the decreased purchasing power
of the currency. It does not take into account the time value of money
(to be discussed)
Example: Market vs. Real Rate
Money in a medium-risk investment makes a guaranteed 8% per
year. Inflation rate has averaged 5.5% per year. What is the real
rate of return on the investment?

Solution
Solve for the real rate i in relation for if
if = i + f + (i)(f)
𝑖𝑓 − 𝑓 0.08 − 0.055
𝑖= =
1+𝑓 1 + 0.055

𝑖 = 0.024 = 2.4%
Two GENERAL ways to work problems when considering
inflation:

(1) Convert to constant value (CV) dollars, then use real rate i.
If f = inflation rate (% per year), the equation is:
Constant-value dollars = future dollars = then-current dollars
(1+ f)t (1+ f)t

(2) Leave money amounts as is and use market rate (interest rate
adjusted for inflation), if
if = i + f + (i)(f)
PW Calculations with Inflation
Two ways to account for inflation in PW calculations

(1) Convert cash flow into constant-value (CV) dollars and use regular i
where: CV = future dollars/(1 + f)t = then-current dollars/(1 + f)t
f = inflation rate
(Note: Calculations up to now have assumed constant-value dollars)

(2) Express cash flow in future (then-current ) dollars and use market
interest rate where if = i + f + (i)(f)
Example: PW with Inflation
A honing machine will have a cost of $25,000 (future cost) six years from
now. Find the PW of the machine, if the real interest rate is 10% per year
and the inflation rate is 5% per year using (a) constant-value dollars,
and (b) future dollars.

Solution: (a Determine constant-value dollars and use i in PW equation

CV = 25,000 / (1 + 0.05)6 = $18,655


PW = 18,655(P/F,10%,6)
= $10,530

(b) Leave as future dollars and use if in PW equation


if = 0.10 + 0.05 + (0.10)(0.05) = 15.5%
PW = 25,000(P/F,15.5%,6)
= $10,530
FW Calculations with Inflation

FW values can have four different interpretations


(1) The actual amount accumulated
 Use if in FW equation FW = PW(F/P, if, n)
(2) The purchasing power in terms of CV dollars of the future amount
 Use if in FW equation and divide by (1+f)t or use real i
where real i = (if – f)/(1 + f) FW = PW(F/P,i,n)
(3) The number of future dollars required to have the same purchasing
power as a dollar today with no time value of money considered
 Use f instead of i in F/P factor FW = PW(F/P,f,n)
(4) The amount required to maintain the purchasing power of the present
sum and earn a stated real rate of return
 Use if in FW equation FW = PW(F/P, if, n)
Example: FW with Inflation
An engineer invests $15,000 in a savings account that pays interest at a
real 8% per year. If the inflation rate is 5% per year, determine (a) the amount
of money that will be accumulated in 10 years, (b) the purchasing power of
the accumulated amount (in terms of today’s dollars), (c) the number of
future dollars that will have the same purchasing power as the
$15,000 today, and (d) the amount to maintain purchasing power and earn a
real 8% per year return.

Solution:
(a) The amount accumulated is a function of the market interest rate, if
if = 0.08 + 0.05 + (0.08)(0.05) = 13.4%

Amount Accumulated = 15,000(F/P,13.4%,10)


= $52,750
Example: FW with Inflation (cont’d)
(b) To find the purchasing power of the accumulated amount deflate
the inflated dollars

Purchasing power = 15,000(F/P,13.4%,10) / (1 + 0.05)10


= $32,384
(c) The number of future dollars required to purchase goods that cost
$15,000 now is the inflated cost of the goods

Number of future dollars = 15,000(F/P,5%,10)


= $24,434

(d) In order to maintain purchasing power and earn a real return, money must
grow by the inflation rate and the interest rate, or if = 13.4%, as in part (a)

FW = 15,000(F/P,13.4%,10)
= $52,750
AW (Capital Recovery) with Inflation

If a small company invests $150,000 in a new production line machine,


how much must it receive each year to recover the investment in 5
years? The real interest rate is 10% and the inflation rate is 4% per year.

The A/P and A/F factors require the use of if when inflation is considered

Solution: Capital recovery (CR) is the AW value


if = 0.10 + 0.04 + (0.10)(0.04) = 14.4%
CR = AW = 150,000(A/P,14.4%,5)
= $44,115 per year
Summary of Important Points
Inflation occurs because value of currency has changed

Inflation reduces purchasing power; one unit buys less


goods ort services
Two ways to account for inflation in economic analyses:
(1) Convert all cash flows into constant-value dollars and use i
(2) Leave cash flows as inflated dollars and use if

During deflation, purchasing power of money is greater in future than


at present
Future worth values can have four different interpretations,
requiring different interest rates to find FW
Use if in calculations involving A/P or A/F when inflation is
considered
14-18
14.1 (a) There is no difference.
(b) Today’s dollars are inflated compared to dollars of 2 years ago.
Therefore, in order
for the dollars to have the same value (i.e., constant-value dollars) as 2
years ago,
divide today’s dollars by (1 + f)2.

14.2 (a) During periods of inflation


(b) During periods of deflation
(c) When inflation is zero

14.3 0.10 = 0.04 + f + 0.04f


1.04f = 0.06
f = 0.0577 or 5.77% per year

14.4 if = 0.20 + 0.05 + (0.20)(0.05)


= 0.26 or 26%
14.5 if per month = 0.30/12 + 0.015 + (0.30/12)(0.015)
= 0.040375 or 4.0375% per month
Nominal if per year = 12(4.0375)
= 48.45% per year

14.6 0.35 = 0.25 + f + 0.25f


1.25f = 0.10
f = 0.08 or 8% per year

14.7 if = 0.04 + 0.01 + (0.04)(0.01)


= 0.0504 or 5.04% per quarter
14.8 if per month = 18/12 = 1.5%
Use inflation-adjusted interest rate equation to solve for i.
0.015 = i + 0.005 + (i)(0.005)
1.005i = 0.01
i = 0.00995 or 0.995% per month

14.9 Let CV = constant-value dollars


CV1 = 45,000/(1 + 0.05)1 = $42,857
CV2 = 45,000/(1 + 0.05)2 = $40,816
CV3 = 45,000/(1 + 0.05)3 = $38,873
CV4 = 45,000/(1 + 0.05)4 = $37,022
14.10 Future, inflated dollars = 10,000(1 + 0.05)10 = $16,289
14.11 Number of future dollars required = 1,500,000(1 + 0.04)30
= $4,865,096
14.12 Assume C1 is the cost today
2C1 = C1(1 + 0.07)n
(1 + 0.07)n = 2.000
n log 1.07 = log 2.000
n = 10.2 years
14.13 0.28 = i + 0.06 + i(0.06)
1.06i = 0.22
i = 0.2075 or 20.75%
14.15 Buying power = 250,000/(1 + 0.04)5
= $205,482
14.16 (a) Constant-value dollars have to increase by only the real
interest rate of 5% per year.
CV5 = 30,000(F/P,5%,5)
= 30,000(1.2763)
= $38,289
(b) if = 0.05 + 0.04 + (0.05)(0.04)
= 9.2%
F = 30,000(F/P,9.2%,5) = 30,000(1.55279)
= $46,584
14.17 Find f using F/P or P/F factor
5400 = 4050(F/P,f,5)
(F/P,f,5) = 1.3333
By factor equation
(1 + f)5 = 1.3333
1 + f = 1.33330.2
1 + f = 1.0592
f = 0.0592 or 5.92% per year
14.24 The two ways to account for inflation in PW calculations are:
(1) Convert all cash flow amounts into constant-value (CV) dollars,
and
(2) Change the interest rate to consider inflation, that is, to account for
the changing
currency value.
14.25 if = 0.10 + 0.04 + (0.10)(0.04)
= 14.4%
PW = 50,000(P/F,14.4%,2)
= 50,000[1/(1.144)2]
= $38,205
14.26 if = 0.10 + 0.04 + (0.10)(0.04)
= 14.4%
PW = 125,000(P/F,14.4%,3)
= 125,000(0.66792)
= $83,490
14.35 if = 0.10 + 0.06 + (0.10)(0.06)
= 16.6% per year
F = 10,000(F/P,16.6%,10)
= 10,000(1 + 0.166)10
= $46,450
14.36 Find F in future dollars using f = -3.0%
F = 50,000(1 – 0.03)5
= 50,000(0.85873)
= $42,937
14.37 Purchasing power = 100,000(F/P,10%,15)/(1 - 0.01)15
= 100,000(4.1772)/0.86006
= $485,687

14.38 Buying power = 60,000(F/A,10%,5)/(1 + 0.04)5


= 60,000(6.1051)/
14.47 Calculate amount needed at 5% inflation rate
and then find A using market rate.
F = 72,000(1 + 0.05)3
= 72,000(1.1576)
= $83,347
A = 83,347(A/F,12%,3)
= 83,347(0.29635)
= $24,700 per year
14.50 if = 0.12 + 0.03 + (0.12)(0.03)
= 15.36%
A = -3,700,000(A/P,15.36%,5)
= -3,700,000(0.30086)
= $-1,113,182 per year
14.51 if = 0.10 + 0.04 + (0.10)(0.04)
= 14.4% per year
A = -40,000(A/P,14.4%,3) - 24,000 + 6000(A/F,14.4%,3)
= -40,000(0.43363) - 24,000 + 6000(0.28963)
= $-39,607 per year

14.52 if = 0.09 + 0.03 + (0.09)(0.03)


= 12.27% per year

A = -180,000(A/P,12.27%,5) - 70,000(P/F,12.27%,3)(A/P,12.27%,5)
= -180,000(0.27927) - 70,000(0.70666)(0.27927)
= $-64,083 per year

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