Paper 1 · Mathematical Reasoning and Aptitude
An amount becomes four times itself in 6 years at a certain rate of interest. In how much time will it become 64 times, the rate remaining unchanged?
A8 years
B16 years
C18 years ✓ Correct
D24 years
Correct answer: (C) 18 years — It will become 64 times in 18 years, so that is the answer.
Explanation
★It will become 64 times in 18 years, so that is the answer.
★The amount becomes four times in 6 years.
★64 times is the same as four times, taken three times over, since 4 cubed is 64.
★Each step of becoming four times takes 6 years.
★So three such steps take 6 times 3 years.
★This gives 18 years.
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