#0, Birthday coincidences
Posted by amchavez on Apr-29-02 at 09:26 PM
I am trying to figure out the probability of 2 students birthdays falling on the same day, out of 28 students. HELP!
#1, RE: Birthday coincidences
Posted by Froment on Apr-30-02 at 07:56 AM
In response to message #0
Hi!
I may help You to determine the probability that AT LEAST two students have the same birthday; I don't know is it interesting for You, but let's see it:
We shall find the probability that all students have different birthdays, let's designate it "q"; then "p", p=1-q, is the probability that AT LEAST TWO students (it means NOT EXACTLY TWO students) have the birthdays fallin' on the same day.
Let's imagine a box with 365 pieces of paper, written "1 January", "2 January", ..., "31 December". You take out one piece, see it and bring back into the box; then You repeat this 27 times more, and if You haven't chosen two same pieces, You won! It's clear that the probability is: q=(365/365)*(364/365)*(363/365)*...*(338/365) = 0,346. Our probability is then: p=1-q = 0,654. (explanation: "338", because 365-27=338).
Hope this helped You? And one more thing: excuse me for my bad english.
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