The simple interest on a certain sum is one-fifth of the sum and the interest rate per cent per annum is 3.2 times the number of years. If the rate of interest increases by 4%, then what will be the simple interest (in ₹) on ₹7,500 for 4 years?

A sum becomes 2215 of itself in 6 years at simple interest. Find the rate of interest per annum.

In how many years will a sum of ₹5,500 amount to ₹6,600 at a simple interest rate of 5% per annum?

A sum of money amounts to ₹16000 in 6 years at simple interest of 25 percent per annum. What will be the total interest for 6 years?