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.