Question 1041613

How many terms ofthe sequence -24, -15, -6, and 3 will give a sum of 1230?
<pre>Use the formula for the SUM of an AP: {{{S[n] = (n/2)(2a[1] + (n - 1)d)}}}, where:
{{{a[1]}}} = First term in AP (- 24 in this case) 
{{{S[n]}}} = Sum of n terms (1,230 in this case)
{{{n}}} = number of terms in the AP (unknown)
{{{d}}} = Common difference (9 in this case)

Thus, {{{S[n] = (n/2)(2a[1] + (n - 1)d)}}} becomes: {{{S[n] = (n/2)(2(- 24) + (n - 1)9)}}}
{{{matrix(1,1, "1,230") = (n/2)(- 48 + 9n - 9)}}} 

Continue to solve for n (the number of terms). You should get {{{highlight_green(matrix(1,2, 20, terms))}}}