Combinations problem

Venk

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Joined
Feb 28, 2019
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So my teacher told us a story about how when she was younger they had a pool of 145 questions for their exam and from these they draw 3 questions for you and hopefully you have studied for them. The thing is one student showed up with having studied for only 6 of the questions. It turned out that he had studied for 3 out of the 3 questions he recieved. What is the chance of that happening and do i calculate this.
 

pka

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Jan 29, 2005
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7,797
So my teacher told us a story about how when she was younger they had a pool of 145 questions for their exam and from these they draw 3 questions for you and hopefully you have studied for them. The thing is one student showed up with having studied for only 6 of the questions. It turned out that he had studied for 3 out of the 3 questions he recieved. What is the chance of that happening and do i calculate this.
Suppose the student chose only six particular, for whatever reasons to study. The student then has \(\displaystyle \dbinom{6}{3}=20\) ways to have studied all three of the questions which will be chosen for him/her.
Now you post what you think. We can help if we know what you understand about this.
 
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