At what rate per cent per annum will a sum of money double in 8 years?

The simple interest on a certain sum at 15% per annum for 5 year is Rs1500 more to the simple interest on the same at 12% per annum for the same period. Find the sum-

In what time will ₹ 72 become ₹ 81 at $$6{1\over4}$$ % per annum simple interest?

A sum of money amounts to 5,200 in 5 years and to 5,680 in 7 years at simple interest. The rate of interest per annum is-

Mahesh invests a sum of money which becomes Rs. 1344 in 3 years and Rs. 1536 in 7 years. How much had he invested?

At some rate of simple interest, A lent ₹ 6,000 to B for 2 years and ₹ 1,500 to C for 4 years and received ₹ 9,00 as interest from both of them together. The rate of interest per annum was

Answer the following questions

At a simple interest Rs. 3050 becomes Rs. 4026 in four years. If the interest rate was increased by 4% how much would Rs.7500 become in four years ?

What is the rate of interest per annum for simple interest at which Rs.880 amounts to Rs.913 in $$1{1\over 2}$$years?