A sum of money amounts to ₹767 in 3 years and to ₹806 in 4 years on simple interest at 6% annum. What is the sum?

₹650

Amount becomes 767 in 3 yrs and 806 in 4 years, it means interest of 1 year = 806 - 767 = 39 Rs.

So, Interest of 3 year = 39 × 3 = 117 Rs.

Here, Principal =  Amount - Interest

                      =  767-117 = Rs 650