Question

Find the sum of a geometric series.

20 - 5 + 5/4 - 5/16 + ...
A) 220/7
B) 16
C) 286/13
D) 66

Answer 1

B edge

Explanation:

Answer 2

Option B.

Explanation:

Consider the given geometric series is

`S=20-5+(5)/(4)-(5)/(16)+...`

We need to find the sum of given series.

Here, first term is a=20 and common ratio is

`r=(-5)/(20)=-(1)/(4)`

The sum of infinite GP is

`S=(a)/(1-r)`

Substitute
`a=20\text{ and }r=(-5)/(20)=-(1)/(4)`.

`S=(20)/(1-(-(1)/(4)))`

`S=(20)/((5)/(4))`

`S=(20* 4)/(5)`

`S=16`

Therefore, the correct option is B.