Question

at what % of simple interest an amount will be double in 5 years​

Answer 1

Answer:

20 per cent per year

Step-by-step explanation:

P = initial amount

R = rate of interest per cent per year = ?

T = time period in years = 5

SI = Simple Interest

A = final amount at the end of period T

SI = (P*R*T)/100

A = P + SI

We want to find R such that amount doubles

This means that:

A = 2P

=> 2P = P + SI

=> P = SI

=> P = (P*R*T)/100

=> 1 = R*T/100

=> R*T = 100

We are given T = 5

=> R*5 = 100

=> R = 20

The given rate of interest will be 20 per cent per year

In general, for doubling of amount in the case of simple interest, we need to simply find pairs of R and T such that their product is 100.

e.g. if we need doubling in 10 years, R = 10; if we need doubling in 20 years, R = 5; if we need doubling at 5 per cent, we will need 20 years, and so on.