Compound Interest

71 If a certain sum at compound interest becomes double in 5 yr, then in how many years, it will be 16 times at the same rate of interest?

72 The difference between CI and SI for 3 years at the rate of 20% pa is ₹ 152. What is the principal lent?

73 The height of a tree increases every year 1/8 times. If the present height of the tree is 64 cm, then what will be it's height after 2 years?

74 The difference between compound interest and simple interest for 2 years at rate of 5% per annum is ₹ 5, then find the sum

75 Pinky borrowed certain sum from Meena for 2 years at simple interest. Pinky lent this sum to Venu at the same rate for 2 years at compound interest. At the end of 2 years, she received ₹ 110 as compound interest but paid ₹ 100 as simple interest. Find the sum and the rate of interest:

76 The population of a town is 126800. It increases by 15% in the first year and decreases by 20% in the second year. What is the population of the town at the end of 2 years?

77 The compound interest is ₹ 6.40 more than the simple interest, if a sum is lent for 2 years at 8% compound interest. Find the sum:

78 What is the difference between compound interest and simple interest for 2 years on the sum of ₹ 1250 at 4% pa?

79 Income of Joyeeta was ₹ 4000. In the first 2 years, his income decreased by 10% and 5% respectively but in the third year, the income increased by 15%. What was his income at the end of third year?

80 At what per cent annual compound interest rate, a certain sum amounts to it's 27 times in 3 years?