Question

Ashok opened a fixed deposit with certain amount in a bank .The sum quadrupled in 8 year at R% annum interest being compounded annually Find the time in which it will become 32 times itself at R% per annum interest being compounded annually (in years)
A. 20
B. 24
C. 16
D. 28

Answer 1

Correct Answer - a
Let the sum be Rs P
`P(1+(R )/(100))^(8)=49`
`(1+(R )/(100)^(8)=4`
`1+(R )/(100)=4^(1//8)`
Let the required time by N year
`P(1+(R )/(100))^(N)=32 P`
`(1+(R )/(100)^(N)=32`
`(4^(1//8))^(N)=32`
`(2^(2))^(N//8)=2^(5)`
`2^(N//4)=2^(5)`
`(N)/(4)=5rarrN=20`