# How do you find the sum of a geometric sequence whose first term is -160, whose last (nth) term is 5, and whose common ratio is -1/2?

Sum $= - 105$

#### Explanation:

The numbers are
$- 160 , 80 , - 40 , 20 , - 10 , 5$

and these numbers may be obtained by multiplying the 1st term by $r = - \frac{1}{2}$and so forth and so on...

Sum$= - 160 + 80 - 40 + 20 - 10 + 5 = - 105$
Sum$= - 105$