You are going to play penny slots at a casino. The slot machine you have picked has 4 reels with 20 different symbols on each reel.
a) What is the probability of the same symbol appearing on all of the reels?
b) What is the probability of winning 1 dollar in the slot machine after spending 5 dollars?
For a), I got (1/20)^3, since it doesn't matter which symbol appears first, the other three just have to match the first symbol.
I am stuck on how to find pi (or probability of success) for b). I understand that n (number of trials) = 500 and x (number of successes) = 100.
The equation for binomials is P(X) = C(n, x)(pi^x)(1-pi)^n-x