Question

Find the sum of the geometric series.

Answer 1

Answer:

40/3  option B

Step-by-step explanation:

20-10+5-5/2+ ...

We need to find the sum of infinite geometric series

$S_n = \frac{a}{1-r}$

a is the first term (20)

r is the common ratio

To find common ratio we divide second term by first term

r=$\frac{-10}{20} = -\frac{1}{2}$

now we plug in the values

$S_n = \frac{20}{1-(-\frac{1}{2}}$

$S_n = \frac{20}{1+\frac{1}{2}}$

$S_n = \frac{20}{\frac{3}{2}}$

$S_n = 20 * \frac{2}{3}$

sum = 40/3