A certain sum becomes 4 times of itself in 5 years at a rate of simple interest. In 15 years in will become how many times of itself at the game rate of simple interest?

10

We know ,

Simple Interest = \(\frac{Principal ×Rate × Time }{100}\)

Amount = Principal + Interest

Let principal = P

ATQ,

A sum becomes 4 times of itself in 5 years i.e. 4P

Simple interest in 5 years = 4P - P = 3P

So , 3P = \(\frac{P × Rate × 5 }{100}\)

Rate = 60% In 15 years , Sum becomes = P + \(\frac{P × 60× 15 }{100}\)

= p + \(\frac{P × 3× 15 }{5}\)

= P + 9P

= 10P

So , In 15 years sum becomes 10 times of itself.