SSC CPO SI and ASI 2016 Paper

Question : 120 of 200

Marks: +1, -0

A sum of money placed at compound interest doubles itself in 2 years. In how many years will it become four times of itself?

Solution:

(2) Let the principal be

R s . x

and ratebe

r \%

p.a., then

2 x=x\ (1+\ {R}/{100}\ )^{2} \ ⇒\ (1+\ {R}/{100}\ )^{2}=2

Let the time required to becomefour times be t years.

\ (1+ {R}/{100}\ )^{t}=4=2^{2}

=\ ( (1+\ {R}/{100}\ )^{2}\ )^{2}=\ (1+\ {R}/{100}\ )^{4}

Therefore,

t=4

years.

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