A sum of money doubles itself in 4 years at compound interest. It will amount to 8 times itself at the same rate of interest in :
Options:
A . 24 years
B . 18 years
C . 16 years
D . 12 years
Answer: Option D Answer: (d)A sum of Rs.x becomes Rs.2x in 4 years.Similarly, Rs.2x will become 2 × 2x= Rs.4x in next 4 years and Rs.4x will become2 × 4x = Rs.8x in yet another 4 years.So, the total time = 4 + 4 + 4 = 12 yearsUsing Rule 5,A certain sum becomes 'm' times of itself in 't' years on compound interest then the time it will take to become mn times of itself is t × n years.
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