Events & Promotions
|
|
GMAT Club Daily Prep
Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.
Customized
for You
Track
Your Progress
Practice
Pays
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Apr 2610:00 AM EDT
-11:00 AM EDT
The Target Test Prep course represents a quantum leap forward in GMAT preparation, a radical reinterpretation of the way that students should study. Try before you buy with a 5-day, full-access trial of the course for FREE!
Apr 2711:00 AM EDT
-12:00 PM EDT
Prefer video-based learning? The Target Test Prep OnDemand course is a one-of-a-kind video masterclass featuring 400 hours of lecture-style teaching by Scott Woodbury-Stewart, founder of Target Test Prep and one of the most accomplished GMAT instructors
Apr 2808:00 AM PDT
-11:00 AM PDT
Whether you are just beginning your MBA journey or fine-tuning your path to a 700+ score, GMAT Day is designed to give you a competitive edge.
17 May 2011, 06:36
Kudos
Bookmarks
D
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
65%
(hard)
Question Stats:
59% (02:06) correct
41%
(02:24)
wrong
based on 265
sessions
History
Date
Time
Result
Not Attempted Yet
A certain freshman class has 600 students and a certain sophomore class has 900 students. Among these students, there are 75 two-person sets of lab partners, each consisting of 1 freshman and 1 sophomore. If 1 student is to be selected at random from each class, what is the probability that the 2 students selected will be a set of lab partners?
(A) 1/75
(B) 1/96
(C) 1/5400
(D) 1/7200
(E) 1/54000
(A) 1/75
(B) 1/96
(C) 1/5400
(D) 1/7200
(E) 1/54000
18 May 2011, 19:08
Kudos
Bookmarks
gmatpapa: As per your request, let me try to explain you the logic here.
Look at the question: "what is the probability that the 2
students selected will be a set of lab partners"
So you see 2 students in front of you - one from freshmen class and the other from sophomore. What is the probability that they are lab partners? There are only 75 pairs of lab partners possible. Total possible pairs are 600*900 (600C1 * 900C1)
So probability = 75/54000 = 1/7200
When you have a question similar to 'There are 4 boys and 3 girls. In how many ways can you make a pair of one boy and one girl?', what do you do? You say we can pick a boy in 4 ways and a girl in 3 ways so total 12 ways.
_ _
B G
There is one spot for a boy and one for a girl. Their positions are defined. As if there were two chairs, a blue one and a pink one for the boy and the girl respectively. So you don't arrange them. You fill the blue chair and the pink one. You don't say "we pick the boy first and then the girl or girl first and then the boy so we get 2 cases, right?"
It is a situation similar to this situation.
Look at the question: "what is the probability that the 2
students selected will be a set of lab partners"
So you see 2 students in front of you - one from freshmen class and the other from sophomore. What is the probability that they are lab partners? There are only 75 pairs of lab partners possible. Total possible pairs are 600*900 (600C1 * 900C1)
So probability = 75/54000 = 1/7200
When you have a question similar to 'There are 4 boys and 3 girls. In how many ways can you make a pair of one boy and one girl?', what do you do? You say we can pick a boy in 4 ways and a girl in 3 ways so total 12 ways.
_ _
B G
There is one spot for a boy and one for a girl. Their positions are defined. As if there were two chairs, a blue one and a pink one for the boy and the girl respectively. So you don't arrange them. You fill the blue chair and the pink one. You don't say "we pick the boy first and then the girl or girl first and then the boy so we get 2 cases, right?"
It is a situation similar to this situation.
General Discussion
17 May 2011, 06:45
Kudos
Bookmarks
Here's how i approached it:
P (picking one of the freshmen who belong to the pair)= \(\frac{75}{600}\)
P(Picking the corresponding sophomore)= \(1*900\)
P (Picking members of a pair)=\(\frac{75}{600}*\frac{1}{900}\)= \(\frac{1}{7200}\)
Now there will be another case wherein we can pick first from the sophomore students then from the freshmen. Probability will be same as above, ie (\(\frac{75}{900}*\frac{1}{600})= \frac{1}{7200}.\)
Hence the probability should be= \(\frac{1}{7200}+\frac{1}{7200}= \frac{1}{3600}.\) Right?
But this is not in the answer choices so I picked D, which is the correct answer. Can someone please tell me where I am going wrong? Thanks!
P (picking one of the freshmen who belong to the pair)= \(\frac{75}{600}\)
P(Picking the corresponding sophomore)= \(1*900\)
P (Picking members of a pair)=\(\frac{75}{600}*\frac{1}{900}\)= \(\frac{1}{7200}\)
Now there will be another case wherein we can pick first from the sophomore students then from the freshmen. Probability will be same as above, ie (\(\frac{75}{900}*\frac{1}{600})= \frac{1}{7200}.\)
Hence the probability should be= \(\frac{1}{7200}+\frac{1}{7200}= \frac{1}{3600}.\) Right?
But this is not in the answer choices so I picked D, which is the correct answer. Can someone please tell me where I am going wrong? Thanks!
