The difference between the simple interest on a certain sum at the rate of 10%pe

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Question
The difference between the simple interest on a certain sum at the rate of 10%per annum for 2 years and compound interest which is compounded every 6 months is Rs.124.05. what is the principal sum
Options
A. Rs.6000
B. Rs.8000
C. Rs.12000
D. none of these

Correct Answer

Rs.8000

Explanation

Compound Interest on P at 10% for 2 years when interest is compounded half-yearly

= $P {(1 + \frac{\frac{R}{2}}{100})}^{2 T} - P = P {(1 + \frac{1}{20})}^{4} - P = P {(\frac{21}{20})}^{4} - P$

Simple Interest on P at 10% for 2 years = $\frac{P R T}{100} = \frac{P � 10 � 2}{100} = \frac{P}{5}$

Given that difference between compound interest and simple interest = 124.05

$P * {(\frac{21}{20})}^{4} - P - \frac{P}{5} = 124.05$

=> $P [{(\frac{21}{20})}^{4} - 1 - \frac{1}{5}] = 124.05$

P=8000