Counting: Grading One professor grades homework by randomly choosing 5 out of 12 homework problems to grade.

(a) How many different groups of 5 problems can be chosen from the 12 problems?

(b) Probability Extension Jerry did only 5 problems of one assignment. What is the probability that the problems he did comprised the group that was selected to be graded?

(c) Silvia did 7 problems. How many different groups of 5 did she complete?

What is the probability that one of the groups of 5 she completed comprised the group selected to be graded?