Question

find the principal if the compound interest compounded annually at rate of 4% p.a. for 2 years is rs. 81.60

compound interest only!
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Answer 1

let p be x

A = P( 1+r/100)^n

so, A = x(1+4/100)^2

A = 52/50x

C.I =A - P

81.6 = 51/50x - x

816/10 = x/50

816×50/10 = x

x = 880

so, P = 880

Answer 2

P=?,R=4%,Y=2,CI=81.60
$81.60 = p(1 + \frac{4}{100} ){2} - p \\ 81.60 = p( \frac{104}{100) ^{2} } ) - 1 \\ 81.60 = ( \frac{10816 }{10000} ) - 1 \\ 81.60 = p(816) \\ p = \frac{81.60}{816} \times 100 = 1000$