Birthday problem

GRE Quant Problem Solving
1

This was discussed in class. One girl even asked this
Even I did it this way, what’s wrong with this method :

Probablility Of 5 people not sharing birthday month

12/12 * 11/12 * 10/12 * 9/12 * 8/12

2

It depends on the framing of the question
If it was “none of them have any birthday month in common”
Then your answer would be correct
Otherwise, if it was “all 5 of them should not share birthday month”
Then you answer would be wrong
because your answer excludes cases where some of them have the same birthday
For eg, September, September, September, September, October is valid for case ii because all of them don’t share a birthday month
but not valid for case i, because some of them do have a birthday month in common

Hope this makes sense

3

Thanks vidishas!
The Question prompt says No one shares a birthday month with ANYONE ELSE.
In that case, Case 1 is correct right?

4

Then your answer would be correct

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