Question

In the United States, length is usually measured in inches, feet, and miles. Most of the rest of the world uses centimeters, meters, and kilometers. Would a 20% grade (referring to the slope of a roadway) in America equal a 20% grade elsewhere? Explain why or why not.

Answer 1

Yes.

Ratios of like quantities don't have units. (The units cancel.)
(1 m)/(100 m) = (1 ft)/(100 ft) = 1% grade -- no matter where you are.