use a proportion to solve

Question

On a? map, the length of a? nature-center trail is 10.5 cm. If the scale is 1 cm to 21? km, what is the actual length of the? trail? Round your answer to the nearest? tenth, if necessary.

Answer 1

The problem states the scale factor: to convert from cm, multiply by 21 and change cm (on map) to km (real world).

 

So 105 cm on map corresponds to 10.5(21) = 220.5 km on Earth.