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# I'm struggling with questions that always carry this format:

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Intern
Joined: 21 Feb 2008
Posts: 43
I'm struggling with questions that always carry this format: [#permalink]

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09 Mar 2008, 16:42
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

I'm struggling with questions that always carry this format:

45% of people buy A, 60% buy B, and 35% buy C. If 10% buy all three, what percentage buys 2?

or

56% like A, 44% like B, and 40% like C. If 30% like A and B, what is the greatest percentage of people who like C, but not A and B.

I know the answers always carry some variation of the formula:
A+B+C-AB-BC-AC-ABC

Although sometimes ABC is added rather than subtracted, and sometimes it is multiplied by 2. I'm really struggling with what this formula is telling me, and how to work with it.

Director
Joined: 10 Sep 2007
Posts: 938
Re: Grouping Question? [#permalink]

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09 Mar 2008, 17:33
Please use set theory, as per inclusion exclusion principle

A union B union C = A + B + C - AB - BC - AC + ABC

Here AB, BC, AC, and ABC are intersection between respective sets.
Re: Grouping Question?   [#permalink] 09 Mar 2008, 17:33
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# I'm struggling with questions that always carry this format:

 post reply Question banks Downloads My Bookmarks Reviews Important topics

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