Question

A sum of money becomes8/5 of itself in 5 years at a certain rate of simple interest.find the rate of interest

Answer 1

let the principle be P
A/Q
A=5/8P
given T=5years
we know that S.I.=A-P
=8P/5 -P
S.I.=3P/5
S.I.=PRT/100
3P/5=PRT/100
3/5=5R/100
R=3*20/5
R=3*4
R=12
So, the rate is 12%

Answer 2

Here is the answer.

Let the sum of money be P
Then, Amount = 8/5 of P =8/5P
Time = 5 years
Simple Interest = Amount - Sum
Simple Interest = 8/5 P - P = 8-5/5 =3/5 P
$simple \: interest \: = \frac{p \times r \times t}{100}$
$rate \: of \: interest \: = \frac{ simple \: interest \: \times 100}{sum \: \times time}$
$rate \: of \: interest \: = \frac{3p \times 100}{5 \times p \times 5}$
Therefore,
Rate of interest =12%

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