Rohit invests a sum of money at compound interest which doubles itself in 3 years, find in how many years will it amount to four times itself ?
Choose the correct choice from the following choices:
A) 6  B) 7  C) 8  D) 9  E) 2
Explanation:   Case (I) When Time (T) = 3 years, principle P becomes 2P.   Therefore, amount = 2P   6 = P (1 + R/100)T   2P = P (1 + R/100)3   (1 + R/100)3 = 2   (1 + R/100) = 3√2 -------- (6)   (III) Find T for which P becomes 4P   When Time = X and 6mount = 4P   4P = P (1 + R/100)X   (1 + R/100)X = 4   (1 + R/100) = 41/X --------- (B)   Equating (6) and (B) we get,   41/X = 3√2 = 21/3   22/X = 21/3   2/X = 1/3   X = 6 years   6NSWER: 6
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Rohit invests a sum of money at compound interest which doubles itself in 3 years, find in how many years will it amount to four times itself ?