Math Is Fun Forum
  Discussion about math, puzzles, games and fun.   Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ • π ƒ -¹ ² ³ °

You are not logged in.

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

mathsyperson
Moderator
Registered: 2005-06-22
Posts: 4,900

Question by antgaudi

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. dunno


Why did the vector cross the road?
It wanted to be normal.

Offline

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

John E. Franklin
Member
Registered: 2005-08-29
Posts: 3,588

Re: Question by antgaudi

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


igloo myrtilles fourmis

Offline

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

Dross
Member
Registered: 2006-08-24
Posts: 325

Re: Question by antgaudi

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?


Bad speling makes me [sic]

Offline

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

John E. Franklin
Member
Registered: 2005-08-29
Posts: 3,588

Re: Question by antgaudi

See tiny depiction.

View Image: venn.png

igloo myrtilles fourmis

Offline

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

mathsyperson
Moderator
Registered: 2005-06-22
Posts: 4,900

Re: Question by antgaudi

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.


Why did the vector cross the road?
It wanted to be normal.

Offline

Board footer

Powered by FluxBB