compound interest rate - Wikitechy https://www.wikitechy.com/interview-questions/tag/compound-interest-rate/ Interview Questions Tue, 07 Sep 2021 06:05:20 +0000 en-US hourly 1 https://wordpress.org/?v=6.9.4 https://www.wikitechy.com/interview-questions/wp-content/uploads/2025/10/cropped-wikitechy-icon-32x32.png compound interest rate - Wikitechy https://www.wikitechy.com/interview-questions/tag/compound-interest-rate/ 32 32 A sum of money place at compound interest doubles itself in 4 years. In how many years will it amount to eight times itself ? https://www.wikitechy.com/interview-questions/compound-interest/a-sum-of-money-place-at-compound-interest-doubles-itself-in-4-years-in-how-many-years-will-it-amount-to-eight-times-itself/ https://www.wikitechy.com/interview-questions/compound-interest/a-sum-of-money-place-at-compound-interest-doubles-itself-in-4-years-in-how-many-years-will-it-amount-to-eight-times-itself/#respond Tue, 17 Aug 2021 14:36:54 +0000 https://www.wikitechy.com/interview-questions/?p=1782

A sum of money place at compound interest doubles itself in 4 years. In how many years will it amount to eight times itself ?

A. 16

B. 8

C. 12

D. 20

Answer : C. 12…

Explanation :

Let, Principal = Rs. 100.
Amount = Rs. 200.
Rate = r%
Time = 4 years.

Now,
A = P * [ 1 + (r/100) ]n
200 = 100 * [ 1 + (r/100) ]4
2 = [1 + (r/100)]4 ……….. (i)
If sum become 8 times in the time n years, then,
8 = ( 1 + (r/100) )n
23 = ( 1 + (r/100) )n …….. (ii)

Using eqn (i) in (ii), we get
( [1 + (r/100) ]4)3 = ( 1 + (r/100) )n
[1 + (r/100)]12 = (1 + (r/100))n
n = 12 years.

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