Question

A sum of money doubles in 12 years. In how many years it will treble at s.I

Answer 1

, SI ∝ T when rate(R) and principal (P) are constants

Let x be the sum of money and which will treble in n years

(Please note that when the money doubles, simple interest is 2x - x = x

and when the money trebles, simple interest is 3x - x = 2x)

(2x-x) ∝ 12

=> x ∝ 12 -------------(1)

(3x-x) ∝ n

=> 2x ∝ n -------------(2)

From (1) and (2),

x2x=12n12=12n⇒n = 24 yearsx2x=12n12=12n⇒n = 24 years

i.e, in 24 years, the money will treble.