30% off $100 = $70. You save $30.
Equation: $100 − (30% × $100) = $100 − $30 = $70.
Another way to read it: you pay 70% of the original price — that's $70.
$70. The discount is $30 and the final price you pay is $70.
You pay $70 (before tax). That's $100 minus a $30 discount.