ABC26GN4192 · Compound Interest
Subject: General Aptitude · Chapter: Compound Interest · Exam: 2010 · Marks: · Difficulty:
A sum of money at compound interest doubles itself in 15 years. It will become eight times of itself in
(a)45 years
(b)48 years
(c)54 years
(d)60 years
Answer
Explanation
$P\left(1+\frac{R}{100}\right)^{15}=2 P \Rightarrow\left(1+\frac{R}{100}\right)^{15}=2$ Let $P\left(1+\frac{R}{100}\right)^{n}=8 P$ $$\begin{aligned} & \Rightarrow\left(1+\frac{R}{100}\right)^{n}=8=2^{3}=\left\{\left(1+\frac{R}{100}\right)^{15}\right\}^{3} \\ & \Rightarrow\left(1+\frac{R}{100}\right)^{n}=\left(1+\frac{R}{100}\right)^{45} \Rightarrow n=45 . \end{aligned}$$ ∴ Required time $=45$ years.
Explanation as extracted from the printed page; notation may be imperfect.
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