Question

At what rate % per annum of simple interest on a sum be 2/5 of its amount in 10 years?

Answer 1

Let the amount invested be P

Interest rate be R

n = 10 years

We know that simple interest formula

for Principal P, interest rate R and years N = PNR/100

Here n = 10(given)

Simple interest = 2/5 times Principal = 2P/5

This is equal to PNR/100 = 10PR/100

Equating these two we get

2P/5 = 10PR/100

R =4%