# Math Help - Advanced Probability, urgent for tomorrow's test

1. ## Advanced Probability, urgent for tomorrow's test

I have a test tomorrow, and I am not able to figure out how to do problems of this type:

1. In a paint store, there are x white paint cans of Brand A; y white paint cans of brand B; and z white paint cans of brand C. If 3 customers bought 4 white paint cans, what is the probability that they bought 1 can of brand A, 1 can of brand B and 2 cans of brand C.

2. Also, how do you find the same probability (problem 1) using probability distribution functions?

3. In a normal distribution with 15, 22% score more than 17. What is the standard deviation of this distribution? (maximum is not given and in previous problems, the mean and standard deviation were given. We calculated the z-score and used a table to find the corresponding probability).

I would really appreciate any help - I just cannot understand these problems.

Thanks
-sri

2. Thanks, but I did not understand how you came to 4+3-1.

I thought this would be the total cans available x+y+z.

Please correct me if I am wrong.

I really appreciate your effort in helping me.

Thanks.

Also, I do not know the answer.

3. #1
$\frac {\binom {x} {1} \binom {y} {1} \binom {z} {2}} {\binom {x+y+z} {4}}$