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
we will pick new questions that match your level based on your Timer History
Track Your Progress
every week, we’ll send you an estimated GMAT score based on your performance
Practice Pays
we will pick new questions that match your level based on your Timer History
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:
Do RC/MSR passages scare you? e-GMAT is conducting a masterclass to help you learn – Learn effective reading strategies, Tackle difficult RC & MSR with confidence, and Excel in timed test environment
Join us in a comprehensive talk about the F1 Student Visa process with Travis Feuerbacher, former U.S. Visa Officer and licensed U.S. immigration attorney having expertise working for the U.S. Department of State
Ready to skyrocket your career with an MBA? Get ahead with our curated list of FREE courses and resources to kickstart your journey into business education!
Are you attending an MBA or Masters program outside in the US or Europe and wondering how to finance your studies? In this exclusive conversation, we discuss the collateral-free non-cosigner education loans...
Solve 30 high quality GMAT Focus practice questions in timed conditions. Take this GMAT practise test live with peers, analyze your GMAT study progress, and see where you stand in the GMAT student pool.
After just 3 months of studying with the TTP GMAT Focus course, Conner scored an incredible 755 (Q89/V90/DI83) on the GMAT Focus. In this live interview, he shares how he achieved his outstanding 755 (100%) GMAT Focus score on test day.
What do András from Hungary, Pablo from Mexico, Conner from the United States, Giorgio from Italy, Leo from Germany, and Rishab from India have in common? They all earned top scores on the GMAT Focus Edition using the Target Test Prep course!
Join us for an exclusive one-day event focused on mastering the GMAT and maximizing your preparation resources! Here's what you can expect: Don't miss out on this invaluable opportunity to supercharge your GMAT preparation journey.
GMAT Club Hardest Questions: Probability and Combinatorics
[#permalink]
26 Mar 2011, 07:17
I was just working on the set of probability and combinatorics questions from the GMAT Club hardest questions set. I have a question about #13:
A committee of 3 has to be formed randomly from a group of 6 people. If Tom and Mary are in this group of 6, what is the probability that Tom will be selected into the committee but Mary will not?
Does the order of selection matter here? The official answer states: Look for any of the three variants: Tom-notMary-notMary, notMary-Tom-notMary, notMary-notMary-Tom. But if we are just choosing 3 people, why does the "variants" matter. I am having difficulty understanding when permutations matter and when they do not. I was thinking that Tom must be on the committee, that leaves 2 spots available. Mary can't be on the committee, so that leaves 4 available people to choose from. Hence I did, 4 choose 2 as the number of ways to select the committee. The total number of ways to select the committee of 3 without restrictions would then be 6 choose 3.
Is my thinking way off?
Archived Topic
Hi there,
Archived GMAT Club Tests question - no more replies possible.
Re: GMAT Club Hardest Questions: Probability and Combinatorics
[#permalink]
26 Mar 2011, 09:22
mbizhtk wrote:
I was just working on the set of probability and combinatorics questions from the GMAT Club hardest questions set. I have a question about #13:
A committee of 3 has to be formed randomly from a group of 6 people. If Tom and Mary are in this group of 6, what is the probability that Tom will be selected into the committee but Mary will not?
Does the order of selection matter here? The official answer states: Look for any of the three variants: Tom-notMary-notMary, notMary-Tom-notMary, notMary-notMary-Tom. But if we are just choosing 3 people, why does the "variants" matter. I am having difficulty understanding when permutations matter and when they do not. I was thinking that Tom must be on the committee, that leaves 2 spots available. Mary can't be on the committee, so that leaves 4 available people to choose from. Hence I did, 4 choose 2 as the number of ways to select the committee. The total number of ways to select the committee of 3 without restrictions would then be 6 choose 3.
Is my thinking way off?
Both methods would be correct. Yours faster, elegant and less hairy.