Puneet has a recurring deposit account in the Bank of Baroda and deposits ₹ 140 per month for 4 years. If he gets ₹ 8092 on maturity, find the rate of interest given by the bank.

Let rate of interest given by bank = x%.

So,

P = ₹ 140, n = (4 × 12) = 48 months and r = x%

I = $P \times \dfrac{n(n + 1)}{2 \times 12} \times \dfrac{r}{100}$

$\therefore I = ₹ 140 \times \dfrac{48 \times 49}{2 \times 12} \times \dfrac{x}{100} \\[1em] = ₹ 140 \times \dfrac{98x}{100} \\[1em] = ₹ \dfrac{13720x}{100}$

Maturity value = Sum deposited + Interest

= $₹ 140 \times 48 + ₹\dfrac{13720x}{100} = ₹6720 + ₹\dfrac{13720x}{100}$

Given, maturity value = ₹ 8092.

$\therefore 6720 + \dfrac{13720x}{100} = 8092 \\[1em] \Rightarrow \dfrac{13720x}{100} = 8092 - 6720 \\[1em] \Rightarrow \dfrac{13720x}{100} = 1372 \\[1em] \Rightarrow x = \dfrac{1372 \times 100}{13720} = 10.$

Hence, the rate of interest given by bank is 10%.