10% off $500 = $450. You save $50.
Equation: $500 − (10% × $500) = $500 − $50 = $450.
Another way to read it: you pay 90% of the original price — that's $450.
$450. The discount is $50 and the final price you pay is $450.
You pay $450 (before tax). That's $500 minus a $50 discount.