Combinations/Ratios question

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frumpychic: Newbie | Next Rank: 10 Posts; Posts: 8; Joined: Wed Nov 02, 2011 7:17 am

by frumpychic » Wed Nov 02, 2011 7:26 am

From a group of 20 people, what is the ratio of the different teams of 4 that can be selected to the different groups of 5 people teams that can be selected?

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Source: Beat The GMAT — Problem Solving | Wed Nov 02, 2011 7:26 am

shankar.ashwin: Legendary Member; Posts: 966; Joined: Sat Jan 02, 2010 8:06 amFollowed by: 21 members; Thanked: 230 times

by shankar.ashwin » Wed Nov 02, 2011 7:32 am

5 people teams possible;

20C5 * 15C5 * 10C5 * 5C5 / 4!

4 people teams possible;

20C4 * 16C4 * 12C4 * 8C4 * 4C4 / 5!.

You need to find ratio between both.

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neelgandham: Community Manager; Posts: 1060; Joined: Fri May 13, 2011 6:46 amFollowed by: 52 members; Location: Utrecht, The Netherlands; Thanked: 318 times

by neelgandham » Wed Nov 02, 2011 7:37 am

[spoiler]5/16 [/spoiler] ?

Anil Gandham
Welcome to BEATtheGMAT | Photography | Getting Started | BTG Community rules | MBA Watch
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shankar.ashwin: Legendary Member; Posts: 966; Joined: Sat Jan 02, 2010 8:06 amFollowed by: 21 members; Thanked: 230 times

by shankar.ashwin » Wed Nov 02, 2011 7:48 am

Is it just 20C5/20C4? I was assuming all 20 people be formed into teams of 5 and 4. That would be way too big a number..

neelgandham wrote:[spoiler]5/16 [/spoiler] ?

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frumpychic: Newbie | Next Rank: 10 Posts; Posts: 8; Joined: Wed Nov 02, 2011 7:17 am

by frumpychic » Wed Nov 02, 2011 7:49 am

why is it not 20C4/20C5 ?

Last edited by frumpychic on Wed Nov 02, 2011 8:00 am, edited 1 time in total.

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GmatMathPro: GMAT Instructor; Posts: 349; Joined: Wed Sep 28, 2011 3:38 pmFollowed by: 54 members; Location: Austin, TX; Thanked: 236 times; GMAT Score:770

by GmatMathPro » Wed Nov 02, 2011 7:53 am

I think it's 20C4/20C5=[spoiler]5/16[/spoiler]

Pete Ackley
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neelgandham: Community Manager; Posts: 1060; Joined: Fri May 13, 2011 6:46 amFollowed by: 52 members; Location: Utrecht, The Netherlands; Thanked: 318 times

by neelgandham » Wed Nov 02, 2011 8:01 am

shankar.ashwin wrote:Is it just 20C5/20C4? I was assuming all 20 people be formed into teams of 5 and 4. That would be way too big a number..

neelgandham wrote:[spoiler]5/16 [/spoiler] ?

I don't think the question asked the total number of ways in which 20 people can be arranged in 5 teams of 4 each. It just said 'different teams of 4'

Anil Gandham
Welcome to BEATtheGMAT | Photography | Getting Started | BTG Community rules | MBA Watch
Check out GMAT Prep Now's online course at https://www.gmatprepnow.com/

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