Numbers - Math

<?php
$number = 10;
$number = $number + 1;
echo "$number";
?>

11

<?php
$first_number = 10 - 4 / 2;
$second_number = (10 - 4) / 2;
echo "$first_number <br />";
echo "$second_number";
?>

8
3

<?php
$number = 10;
$number++;    // that is the same as saying $number=$number+1;
echo "$number";
?>

11

<?php
$number = 10;
$number--;    // that is the same as saying $number=$number-1;
echo "$number";
?>

9