Hi All,

The 'math' behind this question can be approached in a couple of different ways - and you can actually avoid using the Combination Formula altogether.

The prompt tells us that there are 6 hardcover books and 2 paperback books. We're asked for the probability of selecting AT LEAST one paperback book when we randomly select 4 books from the overall group of 8 books. Since the question focuses on getting AT LEAST one paperback book, we can determine what we DON'T want (meaning 0 paperback books) and subtract that result from 1 (to determine what we DO want).

Working one book at a time, the probability of NOT getting a paperback book is....

1st book = 6/8 chance of NOT getting a paperback

2nd book = 5/7 chance of NOT getting a paperback

3rd book = 4/6 chance of NOT getting a paperback

4th book = 3/5 chance of NOT getting a paperback

Thus, the probability of NOT getting a paperback book for the first 4 books is (6/8)(5/7)(4/6)(3/5). You should notice that the 6s and 5s 'cancel out', leaving us with...

(4)(3)/(8)(7) = 12/56 = 3/14

Thus, the probability of getting AT LEAST one paperback would be 1 - 3/14 = 11/14

Final Answer:

GMAT assassins aren't born, they're made,

Rich

_________________

760+: Learn What GMAT Assassins Do to Score at the Highest Levels

Contact Rich at: Rich.C@empowergmat.com

# Rich Cohen

Co-Founder & GMAT Assassin

Special Offer:

Save $75 + GMAT Club Tests Free
Official GMAT Exam Packs + 70 Pt. Improvement Guarantee

www.empowergmat.com/
*****Select EMPOWERgmat Courses now include ALL 6 Official GMAC CATs!*****