Set Theory : Cardinal numbers

Study concepts, example questions & explanations for Set Theory

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Example Questions

Example Question #1 : Cardinal Numbers

Given the set \displaystyle A, calculate the cardinality.

\displaystyle A=\begin{Bmatrix} 3,7,5,4,9,11,24 \end{Bmatrix}

Possible Answers:

\displaystyle |A|=21

\displaystyle |A|=11

\displaystyle |A|=7

\displaystyle |A|=9

\displaystyle |A|=8

Correct answer:

\displaystyle |A|=7

Explanation:

Given a set \displaystyle W, the cardinality is the number of elements in \displaystyle W. This is also written as \displaystyle |W|.

Looking at this particular problem, 

\displaystyle A=\begin{Bmatrix} 3,7,5,4,9,11,24 \end{Bmatrix}

Therefore the number of elements in a is,

\displaystyle |A|=7

Example Question #2 : Cardinal Numbers

Given the set \displaystyle A, calculate the cardinality.

\displaystyle A=\begin{Bmatrix} a,a,b,c,d,e,e \end{Bmatrix}

Possible Answers:

\displaystyle |A|=\frac{a+e}{7}

\displaystyle |A|=5

\displaystyle |A|=c

\displaystyle |A|=a

\displaystyle |A|=7

Correct answer:

\displaystyle |A|=5

Explanation:

Given a set \displaystyle W, the cardinality is the number of elements in \displaystyle W. This is also written as \displaystyle |W|.

Looking at this particular problem, 

\displaystyle A=\begin{Bmatrix} a,a,b,c,d,e,e \end{Bmatrix}

First, rewrite the set to depict a more accurate description of the space.

\displaystyle A=\begin{Bmatrix} a,b,c,d,e \end{Bmatrix}

Therefore, counting up the number of elements, results in the following cardinality,

\displaystyle |A|=5

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