50% off $100 = $50. You save $50.
Equation: $100 − (50% × $100) = $100 − $50 = $50.
Another way to read it: you pay 50% of the original price — that's $50.
$50. The discount is $50 and the final price you pay is $50.
You pay $50 (before tax). That's $100 minus a $50 discount.