The sum of money placed at a compound interest doubles itself in 4 years. In how many years will it amount to eight times itself?

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answer is C.

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Detailed Solution

Concept: Compound interest involves both principal amount and the interest gained in the time period.

A: Amount
P: Principal
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n: time period
r: rate
After 4 years A will be twice the principal amount.
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When the amount is eight times the principal:
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From the first condition we get that,
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Substituting this value in second condition;
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Hence, the correct answer is option 3.

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