Question

If the sum of first 10 terms of an AP is 100, then the sum of the first and the last terms is .

• A. 60
• B. 40
• C. 20
• D. 10

Answer 1

The correct option is C 20

The sum of the first $n$ terms of an arithmetic progression is given by
$S_n=\frac{n}{2}(a+l),$
where $a$ and $l$ are the first and last terms of the AP respectively.
Here, $n=10$ and $S_n=100.$
$⟹100=\frac{10}{2}(a+l)$
$⟹a+l=\frac{100}{5}=20$
$\therefore$ The sum of the first and the last terms of the given AP is 20.