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
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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