Question

For an A.P, first term a = 5 and Common difference d = 3. Find the sum of first 8 terms.

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Answer 1

Sum of first n terms, s
$=\frac{n}{2}(2a+(n-1\left)d\right)$

$=\frac{8}{2}$$(2\times 5+(8-1)\times 3)$
= 4(10 + 21)
$=31\times 4$
= 124