**Problem**

Two teams (A and B) are competing against each other. They proceed to play games in sequence until one of them wins exactly N times. This team is said to be the winner of the sequence.

We have the probability P of the team A winning a single game. Also there can never be a draw.

Given P and N, calculate the probability of A winning the game.

**Solution**

The simplest way to solve this is by recursion. We define a function that calculates the solution after A won

**a**games and B won

**b**games. I used Python to get the exact solution. Code:

def solve(a,b,N,P): #left something out here ;-) return solve(a+1,b,N,P)*(P/Decimal(100)) + solve(a,b+1,N,P)*(Decimal(1)-P/Decimal(100))

See how cool Python is? I believe that you can manage the rest of the solution on your own ;-)

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