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# so with 2 sets, we have: A + B - AB = total where A is those

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Manager
Joined: 14 Jul 2008
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so with 2 sets, we have: A + B - AB = total where A is those [#permalink]  15 Aug 2008, 09:40
so with 2 sets, we have:

A + B - AB = total

where A is those in set A, B is those in set B, and AB is the intersect.

What if we have 3 sets: A, B, C.

Is the correct formula

A + B + C - AB - BC - AC - 2*(ABC) = total

to avoid double counting?
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Re: Venn Diagrams - 3 Sets [#permalink]  15 Aug 2008, 12:15
Should be A + B + C - AB - BC - AC + 3*(ABC) = total

[Edited once for typo]
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Re: Venn Diagrams - 3 Sets [#permalink]  15 Aug 2008, 12:58
PatrickBateman wrote:
so with 2 sets, we have:

A + B - AB = total

where A is those in set A, B is those in set B, and AB is the intersect.

What if we have 3 sets: A, B, C.

Is the correct formula

A + B + C - AB - BC - AC - 2*(ABC) = total

to avoid double counting?

It should be A + B + C - AB - BC - CA + ABC -- when AB BC and CA include intersect of all 3. Note that its only ABC and not 3ABC as mentioned in the previous post.

The formula you quoted is correct if you are considering AB = "A and B alone" no C involved. And similar logic for BC and CA
Manager
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Re: Venn Diagrams - 3 Sets [#permalink]  15 Aug 2008, 15:04
bhushangiri wrote:

It should be A + B + C - AB - BC - CA + ABC -- when AB BC and CA include intersect of all 3. Note that its only ABC and not 3ABC as mentioned in the previous post.

The formula you quoted is correct if you are considering AB = "A and B alone" no C involved. And similar logic for BC and CA

how can I interpret this logically?

We remove AB because we double count them in A, and B.

We add back ABC because we "double remove" them in AB, BC, CA.

Is that sort of the logic?
_________________

I did it all for the Starwood points.

Re: Venn Diagrams - 3 Sets   [#permalink] 15 Aug 2008, 15:04
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# so with 2 sets, we have: A + B - AB = total where A is those

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