A sum lent at simple interest amounts to ₹17,600 after 2 years and to ₹20,800 after 6 years. What is the rate of interest per annum?

Explanation

1. 01

   Interest for the 4 extra years = ₹20,800 − ₹17,600 = ₹3,200, so one year's interest = ₹800.

2. 02

   Principal = ₹17,600 − 2 × ₹800 = ₹16,000.

3. 03

   Rate = $\frac{800}{16000} \times 100 = 5\%$.