Question

A sum of Rs 1,780 become Rs 2,136 in 4 years Find : (1) the rate of interest . (2) the sum that will become Rs 810 in 7 years at the same rate of interest .

Answer 1

Step-by-step explanation:

(i) In first case, Principal (P) = Rs. 1,780

Amount (A) = Rs. 2,136

∴ S.I. = A – P = Rs. 2,136 – 1,780 = Rs. 356

Time (T) = 4 years

∴ Rate = (S.I. × 100)/(P × T) = (356 × 100)/(1780 × 4) = 5% p.a.

(ii) In second case, let principal (P) = Rs.100

Rate (R) = 5% p.a. , Time (T) = 7 years

∴ S.I. = (P × R × T)/100 = (100 × 5 × 7)/100 = Rs. 35

∴ Amount = P + S.I. = Rs. 100 + 35 = Rs. 135

If amount is Rs. 135, then principal = Rs. 100

And if amount is Rs. 810, then principal

= Rs. (100 × 810)/135 = Rs. 600