Gujarati
Hindi
6.Interest
medium

If a sum of money placed at compound interest, compounded annually, doubles itself in $5$ years, then the same amount of money will be $8$ times of itself in (In $years$)

A

$25$

B

$20$

C

$15$

D

$10$

Solution

(c) Let the principal be ₹1.

$\therefore \quad A=P\left(1+\frac{R}{100}\right)^{T}$

$\Rightarrow \quad 2=1\left(1+\frac{R}{100}\right)^{5}$

Cubing both sides,

$2^{3}=\left(1+\frac{R}{100}\right)^{5 \times 3}$

$\Rightarrow \quad 2^{3}=\left(1+\frac{R}{100}\right)^{15}$

$\therefore \quad$ Time $=15$ years

Standard 13
Quantitative Aptitude

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