Question

A certain sum of money doubles itself in ten years, in how many years will it become two and half times at the same rate of simple interest?​

Answer 1

If a sum of money doubles itself in ten years, then the annual rate of simple interest is 100%/10 = 10%.

Let P be the principal amount. After n years at a rate of 10%, the amount becomes:

A = P + (10/100)*P*n
A = P*(1 + 0.1n)

If the amount becomes two and a half times the principal, then:

2.5P = P*(1 + 0.1n)

Dividing both sides by P, we get:

2.5 = 1 + 0.1n

Subtracting 1 from both sides, we get:

1.5 = 0.1n

n = 15

Therefore, the sum of money will become two and a half times at the same rate of simple interest in 15 years.