Question 52

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

Solution

Let the principal be P

If the principal is doubled in 5 years

Then C.I = P in 5 years

Amount=P(1+r%/100)^t

2P= P(1+r%/100)^5

(1+r%/100)^5=2

Then, 8P = P(1+r%/100)^t

8={(1+r%/100)^5}^t/5

2^3 = 2^(t/5)

3=t/5

t = 15

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