If a sum on compound interest becomes three times in 4 years, then with the same interest rate, the sum will become 81 times in:
Choose the correct choice from the following choices:  A) 12 years  B) 18 years  C) 16 years  D) 14 years  E) 19 years
Explanation:   The sum P becomes 3P in 4 years on compound interest   3P = P(1+R/100)4   â‡’ 3 = (1+R/100)4   Let the sum P becomes 81P in n years   81P = P(1+R/100)n   â‡’ 81 = (1+R/100)n   â‡’ (3)4 = (1+R/100)n   â‡’ ((1+R/100)4)4 = (1+R/100)n   â‡’ (1+R/100)16 = (1+R/100)n   n=16   i.e, the sum will become 81 times in 16 years   ANSWER IS 16 years
<result>C</result>
If a sum on compound interest becomes three times in 4 years, then with the same interest rate, the sum will become 81 times in: