Question 98

If an amount doubles in 5 years at compound interest, then the number of years required to make it eight times at the same rate of compound interest is

Solution

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Let say,$$Amount=P$$ and 

$$rate of interest=r percent$$

So, according to the question,

$$P(1+r/100)^5=2×P$$.

$$or,(1+r/100)^5=2$$

So,$$r=14.86 percent$$

let say ,in x years it will become 8 times.

So,

$$P(1+r/100)^x=8P$$

or,$$(1+r/100)^x=2^(15/5)$$

or,$$(1+r/100)^x=(1+r/100)^15$$

So, x=15.

D is correct choice.

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