Chapter 9 · Questions · page 56 of 68
How do you use a map scale?
Short answerA map scale is a ratio. Set up a proportion of map distance to real distance and solve. If 1 inch is 25 miles, 3.5 inches is 87.5 miles.
levelPre-algebra
standard7.G.A.1
practiceProportions
Every distance on the map is the real distance shrunk by the same factor. That makes scale problems proportions with inches on top and miles on the bottom, or the other way round, as long as both fractions match.
How to use it
- Write the scale as a fraction: map units over real units.
- Write the second fraction the same way with the unknown.
- Cross multiply and divide.
Example
Where it goes wrong
- Mixing units, such as inches on one map and centimetres in the scale.
- Dividing when you should multiply. A longer map line always means a longer real distance.