A sum of money doubles itself in five years In how many years will it becomes four fold if interest ...........

Quantitative Aptitude (CDS) Simple Interest

A sum of money doubles itself in five years. In how many years will it becomes four-fold if interest is compounded annually?

5 years

10 years

8 years

9 years

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Explanation:

Let principal money is P
C.I.=P(1+r/100) ^n
2P=P(1+r/100) ^5
2=(1+r/100) ^5
2^1/5=(1+r/100) ... (1)
Second Compounded money
4 P=P(1+r/100) ^n
4 ^1/n=(1+r/100) .... (2)
Divide equation (1) by equation(2)
(1/2)^(1/5 - 2/n)=1
(1/2)^(1/5 - 2/n)=(1/2)^0
(1/2)^ (1/5 - 2/n)=(1/2)^0
1/5 -2/n=0
n=10 yr