Simple Interest

71 Find the simple interest on ₹ 720 at 5 % per annum for 9 months:

72 A certain sum in certain time becomes X 500 at the rate of 8% per annum SI and the same sum amounts to X 200 at the rate of 2% per annum SI in the same duration. Find the sum and time:

73 Alok lent out a certain sum. He lent 1/3 part of his sum at 7% SI, 1/4 part at 8% SI and remaining part at 10% SI. If ₹ 510 is his total interest, then find the money lent out:

74 Find the simple interest on ₹ 2400 at 10 % per annum for 7 months. 

75 What principal will amount to ₹ 16000 in 6 years at 10% simple interest? 

76 A certain sum becomes 3 fold at 4% annual rate of interest. At what rate, it will become 6 fold?

77 A sum becomes two fold in 6 yr at a certain rate of interest. Find the time, in which the same amount will be 10 fold at the same rate of interest:

78 The simple interest on a certain sum of money for 5/2 years at 12% per annum is ₹ 20 less than the simple interest on the same sum for 7/2 years at 10% per annum. Find the sum:

79 Harsha makes a fixed deposit of ₹ 20000 in Bank of India for a period of 3 years. If the rate of interest be 13% SI per annum charged half-yearly, what amount will he get after 42 months?

80 At simple interest, a sum becomes 3 times in 20 yr. Find the time, in which the sum will be double at the same rate of interest: