If the simple interest on a sum of money at 5% p.a. for 3 years is Rs. 1200, the compound interest on the same sum for the same period at the same rate is

A Rs. 1260

B Rs. 1261

C Rs. 1264

D Rs. 1265

E Rs.1226

Solution

Correct Answer: Option B

Let, the sum is P.

We know that, formula for simple interest:

\(S.I.\; = \frac{{P \times R \times T}}{{100}}\)

Where,

S.I. = Simple Interest

P= principal

T = Time

R = Rate of interest

∴ SI = P × (5/100) × 3 = 1200

⇒ P = 8000

We know the formula for compound interest-

\(\Rightarrow {\mathbf{CI}} = \left[ {{\mathbf{P}}\left\{ {{{\left( {1 + \frac{{\mathbf{R}}}{{100}}} \right)}^T} - 1} \right\}} \right]\)

Where,

CI = Compound interest

P = Principal

R = Rate of interest

T = Time period

\(CI\; = \;8000\;\left[ {{{\left( {1\; + \frac{5}{{100}}} \right)}^3}\;-\;1\left] {\; = \;8000} \right[{{\left( {\frac{{21}}{{20}}} \right)}^3}-1} \right]\;\)

∴ CI= 1261

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