A sum of money doubles itself at compound interest in 15 years . In how many years will it become eight times ?
`P(1 + R/100)^15 = 2P rArr (1 + R/100)^15 = (2P)/(P) = 2` ..........................(i)
Let` P(1 + R/100)^n = 8P rArr (1 + R/100)^n = 8 = 2^3 = {(1 + R/100)^15}^3 ` [using (i)]
`rArr (1 + R/100)^n = (1 + R/100)^45`
`rArr n = 45`
Thus, the required time = 45 years
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