In this problem you are converting a true distance (4 km) to a map distance (? cm) using an equivalent,
4 cm = 5 km. Use dimensional analysis to do any conversion:
Dimensional analysis is based on the fact that any number multiplied by 1 does not change the value:
value given x 1 = same value
You can write "1" in several ways: 3/3 or 7.2/7.2 or 12 inches/1 foot or 1 football field/100 yds or ...
These are called conversion factors
Either value in an equivalence can be on the top with the other on the bottom of a conversion factor.
Although 12 in/1 ft and 1 ft/12 in are both equivalent to one, you choose the appropriate conversion factor so that some units will cancel, leaving the desired unit to express your answer:
If you want to convert 163 in to ft: 163 in x 1 ft/12in = 13.6 ft
For your problem, 4 km x 4 cm/5 km = 4x4/5 cm = 3.2 cm
