[162] Find 6 + 9 + 12 + . . . + 30

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Aptitude

TNPSC G4

10th CBSE Maths

Find 6 + 9 + 12 + . . . + 30

162

252

Explanation:

a = 6
l = 30
d = 9 – 6 = 3
n = $n = \dfrac{(l - a)}{d} + 1$
= $\dfrac{(30 - 6)}{3} + 1 $
= $\dfrac{24}{3} + 1 $
= 8 + 1
= 9
Sum, S
=$\dfrac{n}{2}(a+l)$
=$\dfrac{9}{2}(6+30)$
=$\dfrac{9}{2} \times 36 $
=$9 \times 18$
=162

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