Answer:
Sum of the 8 terms = 69.19
Step-by-step explanation:
The sum of the geometric series is S
[tex]s=\frac{a(1-r^n)}{1-r}[/tex]
Where: a is the first term
n is the number of terms
r is the constant ratio.
For the giving geometric series: 120 - 80 + 160/3 - 320/9 + ...
a = 120 , n = 8
r = -80/120 = -2/3
∴ [tex]s = \frac{120(1-(\frac{-2}{3})^8) }{1-(\frac{-2}{3}) } = \frac{50440}{729}=69\frac{139}{729}=69.19[/tex]
