Hello, Mollier!

The wording of the problem is quite fuzzy.

I'll give you my interpretation.

If we have two teams, where one of the teams has a 55% chance of winning,

how many times must the two teams meet so that we can be 95% certain

that the better team winsat least one game?

Let be the stronger team.

Then

The probability thatgames is: .loses

. . and we want this to be less than 5%.

So we have: .

Take logs: .

Divide by , aquantity: .negative

. . and we have: .

Therefore, if they play 4 or more matches,

. . we can be 95% certain that will win a game.