The smallest set $A$ such that $A  \cup  \{1, 2\} = \{1, 2, 3, 5, 9\}$ is

List all the elements of the following sers :

$A = \{ x:x$ is an odd natural number $\} $

Let $S=\{1,2,3, \ldots, 40)$ and let $A$ be a subset of $S$ such that no two elements in $A$ have their sum divisible by 5 . What is the maximum number of elements possible in $A$ ?

Write the following sets in the set-builder form :

${\rm{\{ 2,4,8,16,32\} }}$

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 the set-builder form :

$\{ 1,4,9 \ldots 100\} $