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 Probability
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Principia11
New Member

USA
1 Posts

Posted - 02/13/2012 :  19:02:28  Show Profile  Reply with Quote
I need some help with Probability questions you would find on MathCounts. I good at probability mainly because I dont know the equations for them and I dont know when I use different ones.

Can you give me the way I would set up or start solving this? an equation would be a ton of help

First:

After collecting for the candy drive, Sally had eight 1$-bills, five 5$-bills, and three 10$-bills. She randomly selected three bills without replacement. What is the probability that she chose one of each type of bill?

Edited by - Principia11 on 02/13/2012 19:07:32
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Tessa
Average Member

USA
14 Posts

Posted - 04/24/2012 :  22:53:48  Show Profile  Reply with Quote
Hello Principia11!
Unfortunately, I cannot give you enough help. Would you please reply back with workings? That would really help me. But here's a hint: have you tried using fractions? And I hope you won't mind telling me your grade so that I will know how to give you help appropriate to your year.
Thanks
tessa
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Ultraglide
Advanced Member

Canada
299 Posts

Posted - 04/24/2012 :  23:48:18  Show Profile  Reply with Quote
First of all, let me say that there is no "equation" to solve this problem. You will have to break it down to cases, i.e. 1-5-10; 1-10-5; 5-1-10; 5-10-1; 5-1-10. What I mean by 1-5-10 is the probability of getting a 1 is 8/16, now since a 1 is removed there are 15 left so the probability of getting a 5 is 5/15 and the probability of getting a 10 will be 3/14 so this gives 8/16x5/15x3/14 = 1/28. When you calculate all the probabilities, add them up.
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Tessa
Average Member

USA
14 Posts

Posted - 04/25/2012 :  00:02:23  Show Profile  Reply with Quote
hello ultraglide!
would you mind looking at my two posts in the statistics and probability part(they are new) and answering them?
My username is tessa and the posts are new, so It won't be hard finding my post.
thanks
tessa

Edited by - Tessa on 04/25/2012 00:13:22
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