If in an A.P., first term is 20, common difference is 2 and n^ th… - Vidyadip

MCQ

If in an A.P., first term is 20, common difference is 2 and $n^{th}$ term is 42, then find sum up to n terms.

A
12
B
42
C
352
✓
372

✓

Answer

Correct option: D.

372

372

Solution:
We know, a = 20, d = 2, $a_n$ = 42.
a + (n - 1) d = 42 ⇒ 20 + 2(n - 1) = 42
⇒ 2 (n - 1) = 42 - 20 = 22 ⇒ n - 1 = 11 ⇒ n = 12.
$\text{s}_\text{n}=\frac{\text{n}}{2}(\text{a}+\text{I})\Rightarrow\text{s}=\frac{12}{2}(20+42)=6\times62=372.$

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