Q.What monthly instalment should be deposited in a Recurring Deposit account for 18 months at 8% per annum to receive a maturity value of ₹19,140?

Factor out $P$ from the RD formula and divide the given maturity value by the resulting bracket.

Here $M=₹19{,}140$, $r=8\%$, $n=18$ months, and the monthly instalment $P$ is unknown.

Step 1 — Factor $P$ out of the RD formula.

Step 2 — Evaluate the bracket.

Step 3 — Solve for $P$.

$P = \frac{19{,}140}{19.14} = ₹1{,}000$ …

Rounding the bracket value too early (e.g. rounding $19.14$ down to $19$) before dividing introduces a small but avoidable error into the final instalment figure — …