Question 1041613
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How many terms of the sequence -24, -15, -6, and 3 will give a sum of 1230?
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It is an arithmetic progression, first term is -24, the common difference is 9. 


The sum of the first n terms is equal to

{{{S[n]}}} = {{{(a[1] + ((n-1)*d)/2)*n}}}

(see the lesson <A HREF=https://www.algebra.com/algebra/homework/Sequences-and-series/Arithmetic-progressions.lesson>Arithmetic progressions</A> in this site).  Or

{{{1230}}} = {{{(-24 + ((n-1)*9)/2)*n}}}.

Solve this equation for n and get the answer.
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