Question

which term of Gp series whose 5th and 8th terms are 80 and 640 respectively

Answer 1

Answer:

Step-by-step explanation:

Given

5th term=80=a.r^4

6th term=640=a.r^7

…a.r^7=640

a.r^4.r^3=640

80.r^3=640

r^3=8

r=2

g.p. Series are

5,10,20,40,80,160,320,640……………

Answer 2

hey as we know that general term of G.P. is a*r^(n-1)

thus a*r^4 =80
let's call it 1

and similarly
a*r^7= 640
let's call it 2

now on dividing 2/1

we will get r^3 = 8
thus we can say r= 2

putting into 1 we get a = 5
thus the series are 5,10,20....