Question

I'm trying to find the sum of this geometric series but I can't find a common ratio. How do I find it?

1+1/5+1/25+...

Answer 1

you can't see the common ratio between 1, 5, 25?

Hmmm.

a = 1
r = 1/5

S = a/(1-r) = 1/(1 - 1/5) = 1/(4/5) = 5/4

Answer 2

Anyway, if you suspect a geometric series, just divide any term by the preceding term to get the common ratio

(1/5) / 1 = 1/5
(1/25) / (1/5) = 1/5
. . .