We can use number operators on variables that hold number values:

$tadpole_age = 7; $lily_age = 6; $age_difference = $tadpole_age - $lily_age; echo $age_difference; // Prints 1

Let’s look at another example of performing operations with number variables:

$favorite_num = 22; echo $favorite_num + 1; // Prints 23 echo $favorite_num; //Prints 22

In the code above, we created the variable $favorite_num then we used echo to print that value plus 1. Note that we didn’t reassign the value of the $favorite_num variable, so it still had the value 22 when we printed it on the last line.

We reassign number variables using the assignment operator:

$age = 82; echo $age; // Prints: 82 $age = $age + 2; echo $age; // Prints: 84

Let’s do some addition and subtraction with variables!



Can you help? I’m trying to figure out how much more I spent last month than this month. Last month I spent 1187.23 and this month I spent 1089.98. Create the variables $last_month and $this_month and assign them the corresponding numeric values.


Use echo to print the difference between last month’s spending and this month’s.

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