"The scooter is on sale for 90% off the original price. "
90% off meaning the sale price is 1 - 90% = 10% of the original price.
another way is to calculate what 90% of the originial price is; then subtract that from the original price (because its 90% OFF.)
1st method is easier to use because 10% of original price is simply shifting the decimal to the left by one position.