Question 1173921
Determine the sum of the 15 terms of the arithmetic series where the 5th term is 4 and consecutive terms increase by 3. 
A) 195
B) 285
C) 182
D) 169
<pre>With the 5th term being 4, we get: {{{matrix(5,3, a[n], "=", a[1] + (n - 1)d, a[5], "=", a[1] + (5 - 1)3, 4, "=", a[1] + 12, 4 - 12, "=", a[1], - 8, "=", a[1])}}}  
     Formula for the sum of an AP: {{{matrix(1,3, S[n], "=", (n/2)(2a[1] + (n - 1)d))}}}                           
                                   {{{matrix(3,3, S[15], "=", (15/2)(2(- 8) + (15 - 1)3), S[15], "=", (15/2)(- 16 + 14(3)), SS[15], "=", (15/2)(- 16 + 42))}}}
 Sum of the 1st 15 terms of AP, or {{{highlight_green(matrix(1,9, S[15], "=", (15/2)(26), "=", (15/cross(2))13*cross((26)), "=", 195, "(CHOICE", "A)"))}}}