I need help solving

Question

A sample of 4 students is to be selected from a statistics class with 28 students. The class has 10 students who are parents.

1. How many samples of 4 students are possible?
2. How many samples are possible, where all 4 students are parents?
3. If the sample is selected at random, what is the probability that all 4 students in the sample are parents?

Answer 1

combinations of 4 students out of 28 students: C(28,4) or 28!/ (24!4!)

4 students out of 10 parents are in sample and 0 students out of 18 non-parents are in sample:

C(10,4)*C(18,0)

probability 4 students in sample are parents:

C(10,4)*C(18,0)

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C(28,4)