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Find the sum of the first 15 multiples of 8.
Given:
First 15 multiples of 8.
To do:
We have to find the sum of first 15 multiples of 8.
Solution:
First 15 multiples of 8 are:
$8, 16, 24,......, 104, 112, 120$
The above sequence is an A.P.
Here,
First term $a=8$, common difference $d =16-8=8$ and last term $l=120$
We know that,
Sum of first $n$ terms of an A.P. $=\frac{n}{2}(a+l)$
$=\frac{15}{2}( 8+120)$
$=\frac{15}{2}( 128)$
$=15\times64$
$=960$
Therefore, the sum of the first 15 multiples of 8 is 960.
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