There are 10 different hats, what is the probability that if I got 4 of them that I would get at least 2 the same?

Would it be $\displaystyle 1/10 * 1/9 * 1/8 * 1/7$?

Thanks in advance.

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- Feb 2nd 2010, 12:04 PMbigrooCan you check please
There are 10 different hats, what is the probability that if I got 4 of them that I would get at least 2 the same?

Would it be $\displaystyle 1/10 * 1/9 * 1/8 * 1/7$?

Thanks in advance. - Feb 2nd 2010, 12:44 PMDeadstar
Unless I'm missing something then I think more information is needed..?

How many types of hat are there? Post the ENTIRE question. - Feb 2nd 2010, 01:03 PMbigroo
10 types of hat which are equally likely to be got.

- Feb 2nd 2010, 01:06 PMDeadstar
Ok but how many hats are there in total? If there's only ten then you can't get two the same.

- Feb 2nd 2010, 01:10 PMbigroo
Ok I see now, 10 different types of hat but presumably infinite hats in total. The question is ' if you get four attempts you will obtain at least 2 of the same type'.

You only have 4 attempts to choose. - Feb 2nd 2010, 01:28 PMDeadstar
Maybe this is wrong but I think it's...

1-Probability(all hats are different)

So you get your first hat with prob 1.

The prob that the second one is different is 9/10

The prob that the third one is different is 8/10

The prob that the fourth one is different is 7/10

So 1-Probability(all hats are different) = 1-(9/10*8/10*7/10) = 0.496. - Feb 2nd 2010, 02:22 PMPlato
- Feb 2nd 2010, 10:07 PMbigroo
- Feb 3rd 2010, 03:42 AMDeadstar