Question

What is the sum of the series $2.06+2.02+1.98+...+0.78?$

• A. $-12.48$
• B. $22.56$
• C. $-34.89$
• D. $46.86$

Answer 1

The correct option is D $46.86$

First term = a = 2.06
last term, l = 0.78
$a_n=0.78$
Common difference = -0.04
$a_n=a+(n-1)d$
$0.78=2.06+(n-1)(-0.04)$
$0.78-2.06-0.04=-0.04n$
$1.32=0.04n$
n = 33
$S_n=\frac{n}{2}[a+1]$
$S_{33}=\frac{33}{2}[2.06+0.78]$
$S33=16.5\left[2.84\right]$
$S33=46.86$