SOLUTION: what expression represents the sum of the first n multiples of 15 ?

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Question 732951: what expression represents the sum of the first n multiples of 15 ?
Found 2 solutions by lynnlo, ikleyn:
Answer by lynnlo(4176) About Me  (Show Source):
Answer by ikleyn(53428) About Me  (Show Source):
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what expression represents the sum of the first n multiples of 15 ?
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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%2A%28n%2A%28n%2B1%29%2F2%29.   ANSWER

Solved.