Power of Maths: Paper 1 – Section 5 WORKED EXAMPLE
Calculating depreciation
A car bought for €26 000 depreciates by 18% every year. What is its value after 3 years?
At the end of the fi rst year, the value = 82% of €26 000 = €26 000 × 0·82 = €21 320
At the end of the second year, the value = 82% of €21 320 = €21 320 × 0⋅82
= €26 000 × (0⋅82) × (0⋅82) = €26 000 × (0⋅82)2 = €17 482⋅40
At the end of the third year, the value = 82% of €17 482⋅40
= €17 482⋅40 × (0⋅82) = €26 000 × (0⋅82)2 × 0⋅82 = €26 000 × (0⋅82)3 = €14 335⋅57
The general formula for calculating depreciation is given in the Formulae and Tables book:
F = P(1 – i)t
F = fi nal value P = principal ( present value) t = number of depreciation periods i = rate of depreciation as a decimal or fraction
EXAMPLE 12
A washing machine is bought for €580. It depreciates at 15% p.a. What is its value after 5 years? By how much has it depreciated in 5 years?
Solution P = €580 t = 5 years r = 15%
F = P ( 1 − r
____ 100
= 580(0·85)5 = €257⋅35
It has depreciated by €580 – €257⋅35 = €322⋅65.
186 ) t = 580
( 1 − 15 ____
100 ) 5 EXAMPLE 13
Joe bought a scooter for €1500. After 3 years he estimated its value at €768. Calculate the percentage rate of depreciation p.a. using the reducing balance method.
Solution F = €768,
F = P (1 − i)t
768 = 1500(1 – i)3 768
_____ 1500 = 64
1 − i =
i = 1 − 4 __
( 64 ____
125 )
5 = 1 __
_ 3
1
= 4 __
5 5 = 0·2
r = 20% ∴ 20% is the percentage rate of depreciation per annum.
____ 125 = (1 − i ) 3
P = €1500, t = 3
This pattern can be generalised into the depreciation formula:
F = P ( 1 – r
____ 100
) t = P (1 – i) t
F is the fi nal value of the item. P is the initial value of the item.
r is the percentage rate of depreciation per depreciation period. t is the number of depreciation periods. i = r
____ 100 is the decimal rate of depreciation.
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