Module_04 // Scale
RATIOS &
PROPORTIONS
A ratio is just a comparison of two things. A proportion is a promise that the relationship stays the same, even if the numbers get bigger. It's the math of "Zooming In."
Comparison
We can write ratios in three ways:
2 to 3
2 : 3
2 / 3
"For every 2 of these, we have 3 of those."
The Unit Rate
The most useful ratio is "Per One." It helps us compare prices.
$12 for 4 ApplesConfusing
$3 per AppleUnit Rate
Scale Drawings
Maps use ratios (1 inch = 100 miles) to fit the world into your pocket without distorting the shape.
Interactive Lab
The Ratio Machine
Recipe Scaler
Lemons
2
Water (Cups)
3
Proportion Logic
23
=
23
2 × 3 = 6
3 × 2 = 6
3 × 2 = 6
Base Recipe (1x)Party Size (10x)
Scaling Factor: 1x
The Butterfly Method
To solve for a missing number (x) in a proportion, use Cross Multiplication. Multiply the numbers across the diagonal from each other, and set them equal!
34
=x8
3 • 8 = 4 • x
Verification Protocol
Knowledge Check: Scaling1 / 3
Which of the following is an example of a Unit Rate?
Rule Mastery
You can scale and compare any values.