A sum of money at simple interest amounts to Rs. 400 in 4 years and to Rs. 450 in 9 years. Find the rate of interest per annum.

2.77% 2.86% 3% 3.4%

2.77%

P + SI of 4 years = 400             (1) P + SI of 9 years = 450              (2)          (1) - (2) SI of 5 years = 50 SI of 4 years = 40 Principal ⇒ 400- 40 = 360 Rate = \(\frac{40 × 100}{360 × 4}\) = 2.77%