# Thread: First stats course. need help with this problem

1. ## First stats course. need help with this problem

a tree stand has 12 douglas firs, 10 maples, 3 hemlocks, and 7 cedars.

if you randomly select 6 trees, what is the probability that at least 2 of them will be cedar?

2. ## Re: First stats course. need help with this problem

Hi! We are glad that you posted here! This looks like a homework question though. Our homework help policy can be found here. We mainly just want to see what you have tried so far and that you have put some effort into the problem. I would also suggest checking out this thread for some guidelines on smart posting behavior that can help you get answers that are better much more quickly.

3. ## Re: First stats course. need help with this problem

okay cool. so what think i should do is that in order to find the probably of atleast 2, then it is the same as finding 1 - (p of 0) and (p of 1) ?

so once i find p=0 and p=1 do I multiply those probabilities together and then minus them from 1?

p of 0 = 25/32
p of 1 = 7/32

4. ## Re: First stats course. need help with this problem

Use the hypergeomtric formula. http://en.wikipedia.org/wiki/Hyperge...c_distribution.

After you select one tree, the probability of selecting another tree changes since there is no replacement.

5. ## Re: First stats course. need help with this problem

so if p of 0 is 25/32, then p of 1 is 7/31?

6. ## Re: First stats course. need help with this problem

It seems like you are trying to apply a binomial example you probably saw in class or a textbook to this problem. Don't always try to use the same method and think about what the problem is asking. Stephanie is right. Use the hypergeomtric formula. Read about it. It is essentially what you are trying to count.

Think of it this way, you want only two of 7 cedars. Thus there are 2 choose 7 ways to pick 2 of 7 cedars.
You must have 6 trees so 4 of the trees can be anything else. Apply the same logic above.
Multiply the two and divide by the number of unrestricted ways to choose any six trees.

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