A sum of money, invested at a certain rate of simple interest per annum, amounts to ₹720 in 4 years and to ₹800 in 5 years. The sum invested is:

₹400 ₹600 ₹500 ₹360

₹400

Simple interest of 1 year = 800 - 720 = 80 Simple interest of 4 years = 80 × 4 = 320 Sum invested = 720 - 320 = Rs. 400