Question

What is the cardinal number of following sets?

The set of weeks having $8$days.

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 weeks having $8$days.

We know that number of days in a week is exactly $7$.

There is no any week which have $8$ days.

Therefore, The given set is a null or empty set and number of element is null or empty set is zero.

Hence, the cardinal number of the set of weeks having $8$days is $n\left(A\right)=0$.