Question 732951
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what expression represents the sum of the first n multiples of 15 ?
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<pre>
These multiples form arithmetic progression 

    N(k) = 15k,  k = 1, 2, 3, . . . , n.


First term is 15, the common difference is 15.


The sum of the first n terms is

    15*(1 + 2 + 3 + . . . + n) = {{{15*(n*(n+1)/2)}}}.   <U>ANSWER</U>
</pre>

Solved.