A group of n professionals sit at a table at a conference. Before the presentation begins, they all put their cellular phones into a basket in the middle of the table. One of them, Keira, has a white phone. At the end of the presentation, she reaches for a white phone in the basket.

Question

A group of  n  professionals sit at a table at a conference. Before the presentation begins, they all put their cellular phones into a basket in the middle of the table. One of them, Keira, has a white phone. At the end of the presentation, she reaches for a white phone in the basket.

However, she is not the only one who has a white phone. The probabilty of the others at her table having a white phone is  p .

Given that she has picked a white phone, what is the probability that the phone in her hand is actually hers?

Tram · Accepted Answer

Thank you very much fot the hint. So, if I am not wrong, there are (p*(n-1)+1) phones in the basket. The result is 1/(p*(n-1)+1). Now am I right? Thanks

oobleck · Answer

There are p*n white phones. so what do you think?

Tram · Answer

Thanks, so if there are p*n white phones and the phone that she picked was white. It means that it was one of the p*n phones. So the results is 1/(p*n) Am I right?

jayh · Answer

a little hint, the sentence emphasise on the probability of 'others', not including her.