Ahmed has a recurring deposit account in a bank. He deposits ₹2,500 per month for 2 years. If he gets ₹66,250 at the time of maturity, find:

(i) the interest paid by the bank

(ii) the rate of interest.

Given,

P = ₹2,500

n = 2 years = 24 months

Maturity value = ₹66,250

Sum deposited = ₹2,500 x 24 = ₹60,000

Maturity value = Sum deposited + Interest

Interest = Maturity value - Sum deposited

∴ I = ₹66,250 - ₹60,000

I = ₹6,250

Let rate of interest be r %

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

$\therefore I = 2500 \times \dfrac{24 \times 25}{2 \times 12} \times r \\[1em] 6250 = 2500\times \dfrac{600}{24} \times\dfrac{r} {100} \\[1em] 6250\times 100= 2500 \times 25 \times r\\[1em] 625000 = 62500\times r\\[1em] r=\dfrac{625000}{62500}\\[1em] r=10\%$

Hence,(i) Interest earned by Ahmed ₹6,250 (ii) Rate of interest is 10% .