CMAT 2014 Solved Question Paper

Question : 8 of 100

Marks: +1, -0

A sum of amount at r% compound interest doubles in 3 yr. In 9 yr it will be k times of original principal. What is the value of k?

Solution:

(d) Amount, A = P

(1+r/100)^t

\bo\Case I

When amount doubles in 3 yr
∴ A = 2P = P

(1+r/100)^3

⇒ 2 =

(1+r/100)^3

\;\;\;\;\;\;\;\;\;\;\;

.............(i)

\bo\Case \II

When amount becomes K times in 9 yr
A = k⋅p = p

(1+r/100)^9

⇒ k =

(1+r/100)^{3+3}

∴ k =

(2)^3

= 8 times

\;\;\;\;\;\;\;\;\;\;\;

[from Eq. (i)]

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