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