Question by antgaudi

mathsyperson · 2007-02-28 07:32:24

This post was originally posted in an existing topic in the Formulas section, so it has been moved here.

In the future, please create a new topic in the Help Me! section whenever you have a question that you would like help with. Hopefully you'll find this.

antgaudi wrote:

If I have:
U= 200
n(A)=100
n(B)=80
n(A intersects B)=40
How can I obtain n(A complement which intersects B)?
What about n(B complement)?
Thanks.

John E. Franklin · 2007-02-28 08:23:32

Just a guess, but

This assumes that U is everything.
And 60 units are outside of A and B.
And 60 units are outside of AB and in A.
And 40 units are outside of AB and in B.
And 40 units are in both A and B, which is AB.
So 200 = 60 + 60 + 40 + 40

Dross · 2007-02-28 08:26:35

is the number of elements in B that are not in A. You know there are 80 elements in B, and of those, 40 are in A (as ), leaving the remaining 80 - 40 = 40 elements of B not in A, and hence in A[sup]c[/sup].

is the number of elements (out of the entire 200) that are not in B - how many is this?

John E. Franklin · 2007-02-28 08:45:36

See tiny depiction.

mathsyperson · 2007-02-28 09:12:21

Venn Diagrams are a great way to understand problems like these. If you can work purely with formulas and not get confused then fine, but I find that drawing a picture really helps understanding.

If you get any more questions like these, I recommend drawing a Venn Diagram, looking at the region that you want to find, and working it out from there.

Math Is Fun Forum

#1 2007-02-28 07:32:24

Question by antgaudi

#2 2007-02-28 08:23:32

Re: Question by antgaudi

#3 2007-02-28 08:26:35

Re: Question by antgaudi

#4 2007-02-28 08:45:36

Re: Question by antgaudi

#5 2007-02-28 09:12:21

Re: Question by antgaudi

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