The original price of a pair of shoes is $42. The sale price is 20% off the original price. What is the amount off the original price?

So,

We are trying to determine the amount of sale.

Since the sale price is 20% off of $42, we just need to find 20% of $42.

Find 10%.

10% * $42 = $4.20

Multiply that by 2 to find 20%.

$4.20 * 2 = $8.40

The amount off the original price is $8.40.

To find the amount that was taken off the original price, multiply 42 by 0.20 (20% in decimal form).

42*0.20 = $8.40 off the original price.