Question

What is the cardinal number of following sets?

The set of prime number less than $10$

Answer 1

The number of distinct elements in a finite set is called the cardinal number of the set. It is denoted by $n\left(A\right)$

Given set:

The set of a prime number is less than $10$.

The elements of the set of a prime number less than $10$ are $\left\{2,3,5,7\right\}$

The number of elements in the set is $4$

Therefore, the Cardinal number of the set of a prime numbers less than $10$ is $n\left(A\right)=4$

Hence, the cardinal number of the set of a prime number less than $10$ is $4$