Question

use set notation and the listing method to describe the set of all counting numbers less than or equal to 9

Answer 1

The list of counting numbers less than or equal to 9, is:

$1,2,3,4,5,6,7,8,9$

We can write it in set notation with the listing method as:

$\lbrace1,2,3,4,5,6,7,8,9\rbrace$

A descriptional method using set notation is also possible. Let x be a counting number, then this set is given by:

$\lbrace x\in\N|x\le9\rbrace$