Question

A certain sum is invested for a certain time. It amounts to Rs 400 if the rate is 6% per annum. But when invested at a rate of 2% per annum, it amounts to Rs 250. What is the sum?

Answer 1

I = Prt
F = P + I
F = P + Prt
P + 0.02Pt = 250
P + 0.06Pt = 400

P(1 + 0.02t) = 250
P = 250/(1 + 0.02t)

P(1 + 0.06t) = 400
[250/(1 + 0.02t)] * (1 + 0.06t) = 400
1 + 0.06t = (400/250) * (1 + 0.02t)
1 + 0.06t = 1.6 + 0.032t
0.028t = 0.6
t = 21.42857 yr
P = 175

Answer 2

175