Original Price- $80
Discount- 20% which is 0.20
$80 • 0.20 = 16
$80 - 16 = $64
This was how I was taught to do it but I turned 20% into a decimal which is 0.20 and then did 80 times 0.20 which equals 16. From there you minus it by the original price which is $80 and get $64 as your sale price.
Hope that helped
