State whether each of the following set is finite or infinite :
The set of numbers which are multiple of $5$
Write the following sets in roster form :
$B = \{ x:x$ is a natural number less than ${\rm{ }}6\} $
State which of the following sets are finite or infinite :
$\{ x:x \in N$ and $x$ is prime $\} $
State which of the following sets are finite or infinite :
$\{ x:x \in N$ and ${x^2} = 4\} $
Let $S=\{1,2,3,4\}$. The total number of unordered pairs of disjoint subsets of $S$ is equal to