The sum of how many terms of the series 6 + 12 + 18 + 24 + … is 1800
Choose the most appropriate option
A) 16 B) 22 C) 24 D) 18 E) 26
Let the number of terms be N.   Then, according to the formula,   =&gt; 1800 = N/2[2A+(N-1)D] , where A = First-Term, D = Common-Difference.   =&gt; 3600 = N[12 + (N-1)6]   =&gt; 3600 =N[6 + 6N]   =&gt; 6N^2 + 6N - 3600 = 0.   =&gt; 6N^2 + 150N - 144n - 3600 = 0   =&gt; 6N(N + 25)-144(N+25)   =&gt; N = -25, 24   Hence, the number of terms is 24.   ANSWER:22
<result>B</result>
The sum of how many terms of the series 6 + 12 + 18 + 24 + … is 1800