At Least Once Probabilities

Question

You walk into a room with 3 other people in it. What is the probability that one or more of them has a birthday in the same month as yours?



??? (Round to the nearest tenth of a percent.)

Answer 1

Don't confuse yourself with the context. Break it down to numbers.

 

Your birth month is an arbitrary value. It is 1 of any 12 months.

 

The question asks the probability of 1 or more having the same "value" as yours. The key word there is "or". In probability this means...any match.

 

So you have essentially 3 trys to match your "value"

 

Out of 12 possibilities, you have 3 trys.

 

Therefore the probability of any 3 people sharing your same birth month, is 3/12, or 25%