Question

Which term of the series 5, 10, 20, 40, ..... is 1280?
A.10th
B.9th
C.8th
D.None of these

Answer 1

The Answer is...

B. 9th term

Its like 5 * 2 = 10, 10 * 2 = 20, 20 * 2 = 40,...

So, the series is a G.P. in which a = 5 and r = 2.
Let the number of terms be n.
Then, 5 * 2^n - 1 = 1280

2^n - 1 = 256 => 2^8.
n - 1 = 8
n = 9.

Answer 2

Answer:

option B is right answer...remember me in prayers