# Probability question...at least I believe it is.

• Apr 2nd 2012, 09:30 AM
Ever
Probability question...at least I believe it is.
Hello,
I have a question I could never figure out since I would not even know where to begin.
Here it is,
what is the probability that a Mother and Father and their child would all be born on the 7th of the month but of three different months?
This may not be the proper forum for this question, if not I apologize.
To understand me a little better, I was an art student LOL! Philosophy, art, literature ect....Math, grade ten algebra, is all I achieved. Even Bill Nye the science guy could not teach me basic physics in childs terms. Sad.... I guess we all can't be good at the same thing :0)

Ever
• Apr 2nd 2012, 10:22 AM
emakarov
Re: Probability question...at least I believe it is.
Let (F, M, C) be a triple where each of F, M and C is a number from 1 to 365 (birthdays of mother, father, and child, respectively). Then the total number of such triples is 3653. The number of triples where each number corresponds to the 7th of some month is 12 * 11 * 10. Namely, there are 12 variants for mother; for each of those there are 11 variants for father; and for each of the first two there are 10 variants for child. If every triple (F, M, C) is equally likely, then the probability is the ratio $\frac{12\cdot 11\cdot 10}{365^3}\approx0.002\%$.

Note that this probability corresponds to a given day of the month (7th or any other fixed date <= 28). The probability that all three have birthdays on the same day of the month in different months without specifying which day it is will be of course greater (by about a factor of 30).
• Apr 2nd 2012, 12:04 PM
Ever
Re: Probability question...at least I believe it is.
Wow emakarov I actually understood the way you put that!!! :0) Hey maybe I could have done better in math! Thank-you!!
Sometimes it may just take a great teacher! So the answer would be .002%?
Lovely thank-you again so much....after reading some of the other questions here I realized very quickly I was in way, way over my head and did not expect anyone to answer. It seemed to simple.

Again I thank-you
Ever