Percentage Discount given an Original Price of $30 and a Sale Price of $10

Discount Rate = 1 –  
Discount Rate = 1 – 0.3333
Discount Rate = 0.6667
0.6667 Converted to a Percent: 0.6667 = 66.67%
Percentage Discount given an Original Price of $30 and a Sale Price of $10 = 66.67%
Note: Reduction in Price = $30 – $10 = $20