Question

two teams play a series of games, wher both teams have an equal probability of winning each game. its a best- of-five series, so the frist team to win three games is the winner. what is the probability that the series lasts five games

Answer 1

0.375

Explanation:

With equal probability, hence

p for both teams = 0.5

First team to win three games win, probability that series lasts 5 games :

This means after 4 games each of the teams must have won 2 each ; and the series decider will be on the 5th game :

Each team winning two games and any of the teams could be the eventual winner :

From binomial relation :

P(x = x) = nCx * p^x * q^(n-x)

q = 1 - p = 0.5

Team A :

Winning any 2 from 4 and winning the 5th

(4C2 * 0.5^2 * 0.5^2) * 0.5

0.375 * 0.5 = 0.1875

Team B :

(4C2 * 0.5^2 * 0.5^2) * 0.5

0.375 * 0.5 = 0.1875

Hence, the probability that series lasts five games is :

[4C2*0.5^2*0.5^2)*0.5]+[4C2*0.5^2*0.5^2)*0.5]

0.1875 + 0.1875

= 0.375