Assume that there are 7 different issues of Sports Illustrated magazine, 6 different issues of Time, and 2 different issues of Newsweek, including the December 1st issue, on a rack

Question

You choose 4 of them at random.

(1) What is the probability that exactly 3 are issues issue of Sports Illustrated? 

(2) What is the probability that you choose the December 1st issue of Newsweek?

Answer 1

15 issues, so possible ways of choosing 4 are 15 C 4 = 1365

(1) How many ways here ?

3 are Sports Illustrated, you can choose these in 7 C 3 ways ie 35 ways

The other one you can choose from 8 issues, so 8 ways

Total ways = 8 x 35 = 280

Probability = 280 / 1365

(2) Well assume we choose the December 1st issue of Newsweek. That means we choose the other 3 issues from a possible 14, so 14 C 3 ways = 364 ways

So probability = 364 / 1365

Mike