An amount doubles itself in 5 years with simple interest. What is the rate of interest per year?

The simple interest for four years is one fourth of the principal. At the same rate, which amount become Rs.450 total amount in 2 years?

What is the ratio of the simple interest earned on a certain amount at the rate of 21% per annum for 8 years to that earned on the same sum at the same rate for 21 years?  

A sum of ₹ 7, 930 is divided into 3 parts and given at loan at 5 % simple interest to A, B and C for 2, 3 and 4 years respectively. If the amounts of all three are equal after their respective periods of loan, then the A received a loan of 

The simple interest on ₹ 4,000 in 3 years at the rate of x % per annum equals the simple interest on ₹ 5,000 at the rate of 12% per annum in 2 years. The value of x is 

The simple interest of 7 years of money is Rs. 1750. If the rate of interest was 2% more per annum, how much interest would have been higher?

A certain amount of money earns Rs. 540 as simple interest in 3 years. If it earns a compound interest of Rs. 376.20 at the same rate of interest in 2 years, find the amount.