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.

It appears that you are browsing the GMAT Club forum unregistered!

Signing up is free, quick, and confidential.
Join other 500,000 members and get the full benefits of GMAT Club

Registration gives you:

Tests

Take 11 tests and quizzes from GMAT Club and leading GMAT prep companies such as Manhattan GMAT,
Knewton, and others. All are free for GMAT Club members.

Applicant Stats

View detailed applicant stats such as GPA, GMAT score, work experience, location, application
status, and more

Books/Downloads

Download thousands of study notes,
question collections, GMAT Club’s
Grammar and Math books.
All are free!

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:

0% (00:00) correct
0% (00:00) wrong based on 0 sessions

HideShow timer Statistics

This topic is locked. If you want to discuss this question please re-post it in the respective forum.

Hi folks,

I got stuck with the following combinations question:

"10 tennis players are available. Their coach wants to schedule double games (2 players play another 2 players). How many different games can be scheduled?"

I sort of get what you're trying to say! But maybe you can clear up some confusion for me:

Let's say we have 10 tennis players: (A, B, C, D, E, F, G, H, I, J, L)

1) When I select 2 people out of this set, I might end up with (A, E) -- but not (E, A) since we're not talking about permutations... 2) With 2C8, I select 2 people out of 8. Now where I get confused is this: what does 8 mean in this context? Does it preclude the 2 people that I already chose under 1)? Because if it does, I do not need to divide by 2 right?

2) Yes you are right in the first part. The 8 is because the 2 people precluded in 1)

You still must divide by two by two, because when you calculate using C, it already gives you (A,E) but not (E,A). However, you are multiplying and in doing this you are not using the C formula any more, and thus you are counting pairA x pairB twice.

Imagine that you have only 3 PAIRS (not players), X, Y, Z. How many games it is possible?

If you do 3*2 = 6 you are wrong, because you are counting some games twice: X x Y X x Z Y x X Y x Z Z x X Z x Y

As you can see, the bold ones are repeated. That is why you must divide by two. You are not using the formula any more. The formula of Combination is just use in the first part of the problem.

Now is it clear?

If not, you can just ask, ok? Sometimes it is hard to explain only through text....

Thanks a lot. Can you suggest any reference material to improve the permutation and combination? Thank in advance

coelholds wrote:

1) Yes, you are right

2) Yes you are right in the first part. The 8 is because the 2 people precluded in 1)

You still must divide by two by two, because when you calculate using C, it already gives you (A,E) but not (E,A). However, you are multiplying and in doing this you are not using the C formula any more, and thus you are counting pairA x pairB twice.

Imagine that you have only 3 PAIRS (not players), X, Y, Z. How many games it is possible?

If you do 3*2 = 6 you are wrong, because you are counting some games twice: X x Y X x Z Y x X Y x Z Z x X Z x Y

As you can see, the bold ones are repeated. That is why you must divide by two. You are not using the formula any more. The formula of Combination is just use in the first part of the problem.

Now is it clear?

If not, you can just ask, ok? Sometimes it is hard to explain only through text....

www.4GMAT.com offers a combinations and probablility e-book at $6.99. Does anyone have some experience with 4GMAT ebooks? I feel that they're providing very hard questions but the written English is pretty bad sometimes (which probably confuses ppl when they try to understand the question. Plus, GMAT questions are just worded differently)