help

[anyalong78]

Two graduates win the lottery in the same year. What is the probability that they have the same birthday?

 

[Zermelo]

What exactly is troubling you here? Try to explain what is it exactly that you don't understand and need help with. Have you learned about conditional probability? When are two events dependent or independent? What does that mean for the computation of probability?

 

[ISTER_REG]

What is the probability that they have the same birthday?

So the question is, concerning the probability that two persons have the same birthday.
For this we imagine that person A MUST have a birthday on one of the 365 days in the year, for this person A we now simply set a day. I calculate here with the counter probability that both have birthday on another day, i.e. the second person B can celebrate now only on 365-1 = 364 days a birthday, so that BOTH do NOT have birthday on the same day. We have to do here besides with independent events so that one can state the following:

P("both not same birthday") = 365/365 * 364/365,

from this follows:

P("both same birthday") = 1 - P("both not same birthday") = 1 - 365/365 * 364/365 = 1/365

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PS for the Mods: Is it possible to rename the thread? "help" is not a useful title...

 

[HallsofIvy]

The problem is really, "what is the probability two people have the same birthday?". The fact that they both "won the lottery in the same year" is irrelevant since that has nothing to do with their birthday.