# Math Help - Can you check please

1. ## Can 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 $1/10 * 1/9 * 1/8 * 1/7$?

2. Unless I'm missing something then I think more information is needed..?
How many types of hat are there? Post the ENTIRE question.

3. 10 types of hat which are equally likely to be got.

4. Ok but how many hats are there in total? If there's only ten then you can't get two the same.

5. 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.

6. 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.

7. Originally Posted by bigroo
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.
There are $\binom{4+10-1}{4}$ total number of ways to choose four hats.
There are $\binom{10}{4}$ ways to choose four hats all of different types.

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.
So my answer was nearly the same as yours but instead of $1/10$ you have 1.

9. Originally Posted by bigroo
So my answer was nearly the same as yours but instead of $1/10$ you have 1.
Plato will be right.