Question

a sum of money invested at 6 percent per annum simple interest for a certain period of time yields 960 as interest . if this sum had been invested for 5 years more it would have yielded 2160 as interest . find the sum.

Answer 1

Let the sum of money be x and original time be y
So simple Internet for y yrs time=960
x(6%)(y)=960
xy=16000------------(1)
Now simple intrest for y+5 yrs time=2160
x(6%)(y+5)=2160
x(y+5)=36000
xy+5x=36000
From eq(1)
16000+5x=36000
5x=20000
x=4000rs
Put x in eq(1)
4000y=16000
y=4yrs