Disjoint Subsets, Complement, Cardinality

Date: 09/03/97 at 00:59:05
From: Lisa Wang
Subject: Sets Problem

What does this mean: Sets A, B, and C are DISJOINT subsets of the set 
U?

What does disjoint mean?

Please also explain to me other basic sets operations.  (e.g. 
cardinality, complement, etc.)

Date: 09/03/97 at 05:44:39
From: Doctor Mitteldorf
Subject: Re: Sets Problem

Dear Lisa,

The word "disjoint" means that there's no overlap between A and B or 
between B and C or between A and C. They're all completely separate, 
and have no members in common.

The word "cardinality" refers to the number of elements in a set.  
You just count them up - it's that simple.

The word "complement" refers to what's left over after you extract a
subset. For example, if U is the set {1 2 3 4 5} and A is the subset
{1 2 3} then the complement of A is just the set {4 5} of elements 
thatare members of U but not members of A.

-Doctor Mitteldorf,  The Math Forum
 Check out our web site!  http://mathforum.org/dr.math/