There are 27 students on the collage debate team. What is the probabil

Question

There are 27 students on the collage debate team. What is the probability that at least 3 of them have their birthdays in the same month?

A. 0
B. 3/27
C. 3/12
D. 1/2
E. 1

krushna · Answer

worst case 
--------------
even distribution of 27 students' birth months across 12 months..
after 24 students, each month will have 2 students' birthday. The rest 3 students' birthday can go in to any month 
making the count to 3 or more.

So this is always true or the situtaion will exists all the time and hence the probability should be 1 (E)

(put little more description)

Bunuel · Answer

Why do you think that the probability is not 1? It's not clear at all from your post.

septwibowo · Answer

Sure, correct answer. I think we don't need much calculation for this question, just simple logic right?

Similar simple logic question :
In a drawer which contain 23 pcs red socks and 15 pcs white socks, how many minimum socks should we take  without looking  to get one pair with the same color?

manhasnoname · Answer

Sorry. I was doing that by numbers. I totally missed the logic part.

Even if I use numbers, I should arrive at probability of 1. I screwed up caclulation somewhere. It is not worth discussing anymore. My bad. Sorry again.

EMPOWERgmatRichC · Answer

Hi All,

This prompt is more a 'logic' problem than a math question. We have 27 students and 12 potential months in which those 27 students could possibly have their birthdays. It's possible that all 27 birthdays are in the same month or that the birthdays are "spread out" over the 12 months. We're asked for the probability that at least 3 of the birthdays are in the SAME month. Note that the prompt doesn't specify which month - so ANY month will do.

It might help to think in terms of how you might avoid having at least 3 birthdays in the same month. To do that, you would have no more than 2 birthdays per month. Over the course of 12 months, you could place (12)(2) = 24 of the birthdays and not have 3 or more in any given month. However, we have to place 27 birthdays - and if each of the 12 months already has 2 birthdays, then wherever you put those remaining 3 birthdays... there WILL be at least one month that includes at least 3 birthdays. Thus the probability of this outcome is 100% = 1.

Final Answer:  E

GMAT assassins aren't born, they're made, 
Rich

ScottTargetTestPrep · Answer

Since 27/12 = 2 R 3, that means even if the 27 students’ birth months were equally distributed over 12 months of the year, there must be at least one month with 3 students’ birthdays. Therefore, the probability that at least 3 of them have their birthdays in the same month is 1.

Answer: E

ovelbrin · Answer

it MUST BE at least 3 of them have a same birthday month

bumpbot · Answer

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There are 27 students on the collage debate team. What is the probabil

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