Which of the following are sets ? Justify your answer.

The collection of all natural numbers less than $100 .$

The collection of all natural numbers less than $100$ is a well-defined collection because one can definitely identify a number that belongs to this collection.

Hence, this collection is a set.

Write the following sets in the set-builder form :

${\rm{\{ 5,25,125,625\} }}$

List all the elements of the following sers :

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

Which of the following sets are finite or infinite.

$\{1,2,3, \ldots 99,100\}$

The number of elements in the set $\{ (a,\,b):2{a^2} + 3{b^2} = 35,\;a,\,b \in Z\} $, where $Z$ is the set of all integers, is

Which of the following pairs of sets are equal ? Justify your answer.

$\mathrm{X} ,$ the set of letters in $“\mathrm{ALLOY}"$ and $\mathrm{B} ,$ the set of letters in $“\mathrm{LOYAL}”.$