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Question
If one invests Rs. 10,000 in a bank at a rate of interest 8% per annum, how long does it take to double the money by compound interest? [(1.08)5 = 1.47]
Solution
Amount invested = Rs. 10000
Interest rate = `8/100` = 0.08
amount after 1st year = 10000 (1 + 0.08)
= 10000 (1.08)
Value of the amount after n years
= 10000 (1.08)n
= 20000
∴ (1.08)n = 2
(1.08)5 = 1.47 ...[Given]
∴ n = 10 year. (approximately)
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