Cardinality & Types of Subsets (Infinite, Finite, Equal, Empty)

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  • 0:05 Set Review
  • 0:23 Cardinality
  • 1:07 Empty Set
  • 1:33 Finite & Infinite Sets
  • 2:44 Equal & Equivalent Sets
  • 3:34 Lesson Summary
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Lesson Transcript
Instructor: Kathryn Maloney

Kathryn teaches college math. She holds a master's degree in Learning and Technology.

In this video, we will add to our knowledge of sets. We will talk about cardinality, infinite, finite, equal and the empty set. I think you will find these very straightforward, so let's begin.

Set Review

Before we be begin to talk about cardinality and types of subsets, let's review sets. A set is a collection of elements. An element is a collection of anything - numbers, letters, words, or objects. Using math symbols, this means element:

Mathematical symbol for element
mathematical symbol for element


The number of elements in a set is called the cardinality of the set. The cardinality of set V = {car, truck, van, semi} is four. There are four elements in set V.

There are two ways I have seen the symbol for cardinality. The first has straight bars, like the absolute value symbol. In symbols, |V| = 4. The cardinality of set V is 4. The second way I've seen it written is with an n and then the set in parenthesis. In symbols, n(V) = 4. The cardinality of set V is 4.

Empty Set

An empty set is one that is, well, empty. It doesn't have any elements. Let's say set E is an empty set. We can write set E in symbols like this:

Mathematical symbol for an empty set
symbol for empty set

The cardinality of set E is 0. We would write it as |E| = 0. Be warned, zero is not an element in the set; it simply means the set has no elements!

Finite Set

Let's look at the set of primary colors: P = {red, yellow, blue}. We can say that set P is a finite set because it has a finite number of elements. Finite means we can count the number of elements. In this case, set P has 3 elements: red, yellow, and blue. Set P has a cardinality of 3 because there are 3 elements in the set. We would write it as |P|= 3.

Infinite Set

An infinite set is a set with an infinite number of elements. There are two types of infinite sets - countable and uncountable. A countable infinite set is one that can be counted in one sitting, though you may never get to the last number. An example of a countable infinite set is the set of all integers. An uncountable infinite set is one that cannot be counted because it is too large. An example of an uncountable infinite set is the set of all real numbers. The set of all real numbers equals all rational numbers and irrational numbers.

Equal Sets

Equal sets are those that have the exact same elements in both. Let's say set A = {red, blue, orange} and set B = {orange, red, blue}. Then, set A= set B. We can say set A = set B because they have the same elements - red, blue, orange - even though they are not in order.

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