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 options.
A) 12 years	B) 18 years	C) 16 years	D) 14 years	E) 15 years
Explanation:   Let the sum be P   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)n)n   =(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