Question

Given $a_1=100,a_n=50$ and $n=200$. Find their sum using Gauss method.

• A. 15,000
• B. 14,000
• C. 11,000
• D. 12,000

Answer 1

The correct option is A 15,000

Given; $a=100,a_n=50,n=200$
Using Gauss formula,
$S_n=\frac{n}{2}$ [First term + Last term]
$=\frac{200}{2}[100+50]$
$S_n=15,000$