Homework Help!!

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spicc89

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Oct 23, 2010
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Hi!

I'm having some difficulty with the following question, any help would be greatly appreciated!

We were given a set of data (42 scores) - 9/42 are smokers, and 33/42 do not smoke.

There are three questions related to this:

1) What is the probability that a student who is randomly selected from the class is a smoker?
I did 9/42 = .21 or 21%.. Is that correct?

2) If two students are randomly selected from the class, what is the probability that they will both be smokers?
I did 9/42 x 9/42 = 0.04.. Is that correct?

3) If three students are randomly selected from the class, what is the likelihood that at least two of them will be smokers?

Please help!

Thanks!!
 
a) We are not told that this is a population of students. If we randomly draw a student, I'm not sure what that means. Maybe there were only 3 students in the original population and none of them was a smoker. (We can only hope.) P(smoker student) = 0

Assuming the entire population is students:

b) 9/42 - What else would it be? Have you other options? If so, let's see them. Why do you doubt?

c) Are you going to return the first student to the population after the first selection? You may wish to go with (9/42)*(8/41). Finite populations are a little different. With replacement vs. without replacement is a very important consideration.
 
a) The entire population is 42 students - 9 of them smoke, the remainder (33) do not

b) I always doubt myself when it comes to math! I just wanted to make sure that I did it right.

c) It doesn't say whether we are to return the first student to the population or not, that's why I'm having difficulty.
 
What did I do when you failed to tell me they were students? I catalogued teh ambiguity, made an assumption, and continued. Do that when a problem statement is ambiguous. Sometimes, there are only a few possible appropriate assumptions. It may be instructive to make all the assumptions, one at a time, and solve the problem multiple times. Teachers love that! It's called "discovery" or "exploration".

Stop doubting yourself. If you make no deliberate errors, why not assume you did just fine? It's a whole lot better way to go through life.
 
I gave only "stats homework help". If you do what I told you, you WILL improve your Stats grade and your knowledge of the subject. The fact that it will also improve the rest of your life is only a delightful side effect. :)
 
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