Theory of Positive Integers : Cardinality

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Example Questions

Example Question #1 : Cardinality

Which of the following is a classification of a set whose cardinality is infinite?

Possible Answers:

Positively 

Continuously

Negatively

None of the answers

Countably

Correct answer:

Countably

Explanation:

If a set is stated to have infinite cardinality then it will fall one of the following categories,

I. Countably

II. Uncountably 

Countably infinite sets are those that the elements within the set are able to be counted.

For example, the set of natural numbers

is a countably infinite set.

Uncountably infinite sets are those that the elements cannot be counted. 

For example, the set of real numbers,

The reason the set of real numbers is not countable is because there are infinitely many elements between each element. This differs from the natural numbers because in the natural numbers there are no elements between elements.

Therefore the correct solution is "countably".

Example Question #2 : Cardinality

Which of the following is a classification of a set whose cardinality is infinite?

Possible Answers:

None of the answers

Negatively

Positively

Infinitely

Uncountably

Correct answer:

Uncountably

Explanation:

If a set is stated to have infinite cardinality then it will fall one of the following categories,

I. Countably

II. Uncountably 

Countably infinite sets are those that the elements within the set are able to be counted.

For example, the set of natural numbers

is a countably infinite set.

Uncountably infinite sets are those that the elements cannot be counted. 

For example, the set of real numbers,

The reason the set of real numbers is not countable is because there are infinitely many elements between each element. This differs from the natural numbers because in the natural numbers there are no elements between elements.

Therefore the correct solution is "uncountably".

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