Question

Which term of g.p. 5,10,20,40 ......is 1280?

Answer 1

Clearly, 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 * 2n - 1 = 1280

  ⇒ 

2

n - 1

= 256 = 28.
.'. n - 1 = 8  or  n = 9.

Hope that helps u!

Answer 2

Heya,

Solution:-
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 * 2n - 1 = 1280

⇒ 2n - 1
= 256 = 28.

Therefore, n - 1 = 8  or 【 n = 9】 ANSWER...

HOPE IT HELPS:-))