Find the sum of the first 15 multiples of 8. - Vidyadip

Question

Find the sum of the first 15 multiples of 8.

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Answer

Multiples of 8 are
8, 16, 24, ....
Since fifference is same, it is an AP
We need to find sum of first 15 multiples
We use formula
$\text{S}_\text{n}=\frac{\text{n}}{2}(2\text{a}+(\text{n}-1)\text{d})$
Here, n = 15, a = 8 & d = 16 - 8 = 8
Putting values in formula
$\text{S}_\text{n}=\frac{\text{n}}{2}(2\text{a}+(\text{n}-1)\text{d})$
$=\frac{15}{2}(2\times8+(15-1)\times8)$
$=\frac{15}{2}(16+14\times8)$
$=\frac{15}{2}(16+122)$
$=\frac{15}{2}\times128$
$=960$
Therefore, the sum of first 15 multiples of 8 is 960

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