Here is the problem:

Determine constant c so that c(1/4)^n, n = 1,2,3 ...

satisfies p.d.f for R.V.N.

So I state the geometric progression

Sn = ( 1 -r^n / 1 - r)

yielding

1/4 [ 1 - (1/4)^n / 1 - (1/4)]

Then I take the limit of the geometric progression and I get:

1/3

and I conclude 1 = 1/3c so c = 3

does this sound correct.