20% off $25 = $20. You save $5.
Equation: $25 − (20% × $25) = $25 − $5 = $20.
Another way to read it: you pay 80% of the original price — that's $20.
$20. The discount is $5 and the final price you pay is $20.
You pay $20 (before tax). That's $25 minus a $5 discount.