Q.A man saves ₹200 in the first month and increases his savings by ₹50 every subsequent month. Find his total savings over the first 12 months.

The monthly savings form an AP with $a=200, d=50, n=12$; apply the sum formula.

The monthly savings form an AP: $200, 250, 300,\ldots$ with $a=200$, $d=50$, $n=12$ months.

Apply $S_n=\dfrac{n}{2}[2a+(n-1)d]$: $S_{12}=\dfrac{12}{2}\big[2(200)+(12-1)(50)\big]=6\big[400+550\big]=6(950)=5700$. …

A common error is treating this as a GP (multiplying savings by a fixed factor each month) instead of an AP (adding a fixed amount) — read the problem statement carefully: "increases by ₹50" (a fixed AMOUN …