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:	Answers:
A) 12 years  B) 18 years  C) 16 years  D) 14 years  E) 15 years
Explanation:   The sum P becomes 3P in 4 years on compound interest   3P = P(1+R/100)4   ⇒ 3 = (1+R/100)4   Let the sum P becomes 81P in n years   81P = P(1+R/100)n   ⇒ 81 = (1+R/100)n   ⇒ (3)4 = (1+R/100)n   ⇒ ((1+R/100)4)4 = (1+R/100)n   ⇒ (1+R/100)16 = (1+R/100)n   n=16   i.e, the sum will become 81 times in 16 years   Answer: Option 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: