Question

Mohan deposited Rs 300 per month in a cumulative deposit for 2 years. The bank pays him Rs 9000 on maturity. Find the rate of interest.
[4 MARKS]

Answer 1

Formula: 1 Mark
Steps: 2 Marks
Answer: 1 Mark

Given : $x=Rs300$, $n=24$ and maturity value = Rs 9000
Total amount deposited = $Rs(300\times 24)=Rs7200$
Equivalent principal for 1 month,
$P=x\left[\frac{n(n+1)}{2}\right]=Rs\left[\frac{300(24\times 25)}{2}\right]=Rs90000.\therefore Interest=P\times \frac{r}{100}\times \frac{1}{12}=Rs[90000\times \frac{r}{100}\times \frac{1}{12}]=Rs75r$
$\therefore$ Maturity value = Total amount deposited + Interest
$\Rightarrow Rs9000=Rs(7200+75r)\Rightarrow 75r=9000-7200=1800\Rightarrow 75r=1800\Rightarrow r=24\%$
Hence, the required rate of interest is 24%