Lesson · M.1.8
Proportions
How to set up a proportion from two equal ratios and solve it with cross multiplication, using a map-scale example step by step.
ObjectiveM.1.8Read2 minExam weightNumbers and Algebra ≈ 53% of Mathematics
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See editions and pricing →What you will be able to do
- Set up a proportion with matching units in matching positions.
- Solve a proportion using cross multiplication.
- Recognize a directly proportional equation and find its constant of proportionality.
What the lesson concludes
- A proportion sets two ratios equal, with the same unit in the same position on both sides.
- Solve a proportion by cross multiplication, then divide to isolate the unknown.
- A directly proportional equation has the form y equals kx, with no added or subtracted constant.
- The constant of proportionality k is the same number you get from reducing a ratio to a unit rate.
- Set the proportion up carefully before calculating, since the exam calculator only handles the arithmetic, not the setup.