Mrs. Khandelkar invests Rs $900$ every month in a recurring deposit account for a period of $3$ years at a simple interest rate of $8%$ pa.
(a) Find the total interest she will earn at the end of the period.(b) Find the maturity value of her deposits.

From the question it is given that,

Mrs. Khandelkar invests ₹$900$ every month in a recurring deposit account.

Period = $3$ years

We know that, 1 year = $12$ Months

So,  $3$years = $3\times 12=36$ Months

Rate = $8%$ pa

Then, Money deposited = Monthly value × Number of Months

= ₹ $900\times 36$

= ₹ $32,400$ … [equation i]

So, total principal for 1 month

 $=\left[ 900\times (36(36+1)) \right]/2$

$=5,99,400$

(b)

Now, interest

$=(8\times 5,99,400)/(12\times 100)$ … [equation ii]

$=3,996$

For getting maturity amount we have to add both equation (i) and equation (ii)

$=32,400+3,996$

$=36,396$

Therefore, Maturity amount is ₹$36,396$