How many terms of the series 3, -6, +12, – 24, + ….. are needed to make a total of 1-2

^{8}?-
**A.**

12 -
**B.**

10 -
**C.**

9 -
**D.**

8

##### Correct Answer: Option C

##### Explanation

3, -6, +12, -24

a = 3, r = -2

(8n = frac{a(1-r^n)}{1-r}\

∴1-2^8 = frac{3(1-(-2^{n-1}))}{1-(-2)}\

1-2^8 = frac{3(1-(-2^{n-1}))}{3})

1-2^{8} = 1-(-2)^{n-1}

-2^{8} = -2^{n-1}

8 = n-1

n = 9