Question

A bowl contains 5 red balls and 5 blue balls. A woman selects balls at random without looking at them. (a) How many balls must she select (minimum) to be sure of having at least three blue balls?

Answer 1

Answer: 8

Step-by-step explanation: As the woman is not looking and assuming that the probability of taking a red ball is the same of a blue ball, she must select 8 balls to be sure she has at least 3 blue balls.

Because at the case of selecting 5 red balls in the first 5 selects and to have at least 3 blue ones in her hand, she will select the third blue ball at selection number 8.