The classic birthday problem asks how many people are required to ensure a greater than 50% chance of having at least one birthday match, meaning that two or more people share a birthday. The surprisingly small answer, assuming that all birthdays are equally likely and ignoring leap years like 2012, is 23 people.
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What’s the (implicit) equation for “equation”?
See for yourself with this inverse graphing calculator.
Inclusion and Exclusion and the new GMAT
Dublin native Colm Mulcahy has been in the Department of Mathematics at Spelman College since 1988. His interests include algebra, number theory, geometry and mathematical card principles and effects. Follow him on Twitter at @CardColm and also check out @WWMGT.
The last question, under the heading “Two-Part Analysis”, at the end of this NYT article (from July 2011) on the new GMAT seems to be deliberately worded in a way that forces one to read and think very carefully.
It takes a while to even process the question as it’s asked! I’m assuming that was intentional.
I’m curious how “they” intended people to solve this. Exclude impossible answers until only one is still Included? I guess so.