A had borrowed a certain sum of money and at the end of 2 years, he paid back Rs. 21648.64. The loan was taken for 2 years at a 4% rate of interest compounded semiannually. What was the original sum?

A 20000

B 18000

C 16000

D 10000

E None of these

Solution

Correct Answer: Option A

Formula for CI:

\(A\; = \;P\;{\left( {\;1\; + \frac{r}{{100}}} \right)^t}\)

Where A is the amount at the end of time t,

P is the Principal,

t is time,

r is rate

Given, A = 21648.64, t = 2 years, rate = 4%, compounded semi-annually

If compounded semi-annually ‘r’ becomes ‘r/2’ and ‘t’ becomes 2t.

\(A\; = \;P\;{\left( {\;1\; + \frac{r}{{2\; \times \;100}}} \right)^{t \times 2}}\)

\(\Rightarrow \;21648.64\; = \;P{\left( {\;1\; + \frac{4}{{100\; \times \;2}}} \right)^{2\; \times \;2}}\)

⇒ 21648.64 = P( 1 + 0.02 )4

⇒ 21648.64 = P(1.082432)

⇒ P = 20000

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