GMAT prep : probability

This topic has expert replies
Newbie | Next Rank: 10 Posts
Posts: 8
Joined: Sun Jun 03, 2007 10:59 pm

GMAT prep : probability

by sneakpeek » Wed Jun 27, 2007 5:33 pm
A basket contains 5 apples of which 1 is spoiled and the rest are good. If Henry is to select 2 apples from teh basket simultaneously and at random, what is the probability that the 2 apples selected will include the spoiled apple?

User avatar
Master | Next Rank: 500 Posts
Posts: 277
Joined: Sun Jun 17, 2007 2:51 pm
Location: New York, NY
Thanked: 6 times
Followed by:1 members

by givemeanid » Wed Jun 27, 2007 6:59 pm
2/5. What is the OA?

User avatar
Community Manager
Posts: 789
Joined: Sun Jan 28, 2007 3:51 pm
Location: Silicon valley, California
Thanked: 30 times
Followed by:1 members

by jayhawk2001 » Wed Jun 27, 2007 8:41 pm
sneakpeak, can you please post the answer choices along with the
question.

Number of ways in which you can get 1 spoiled apple = 1 * 4C1 = 4

Number of ways to choose 2 apples from a set of 5 = 5C2 = 10

So, probability will be 4/10 = 2/5

Newbie | Next Rank: 10 Posts
Posts: 8
Joined: Sun Jun 03, 2007 10:59 pm

by sneakpeek » Thu Jun 28, 2007 2:18 pm
Answer is 2/5.

Answer choices are
1/5
3/10
2/5
1/2
3/5

Junior | Next Rank: 30 Posts
Posts: 11
Joined: Mon Dec 11, 2006 3:11 pm

by gmatfan » Thu Jun 28, 2007 8:38 pm
Another way to tackle this is the opposite or complement of the probability of chosing 1 bad apple out of two is figuring out the probability of choosing no bad apples and subtracting that from one.

Probability of choosing one good apple....4/5
Probability of choosing second good apple....3/4

4/5 * 3/4 = 12/20

1 - 12/20 = 20/20 - 12/20 = 8/20 = 2/5