Proportions Formula
The Formula
When to use: If 2 candies cost 1, then 4 candies cost 2—same proportion.
Quick Example
Notation
What This Formula Means
An equation stating that two ratios are equal, used to find an unknown when three of the four values are known.
If 2 candies cost 1, then 4 candies cost 2—same proportion.
Formal View
Worked Examples
Example 1
easySolution
- 1 Cross-multiply: 15x = 6 \times 10 = 60.
- 2 Divide both sides by 15: x = \frac{60}{15} = 4.
- 3 Check: \frac{4}{6} = \frac{2}{3} and \frac{10}{15} = \frac{2}{3} \checkmark
Answer
Example 2
mediumExample 3
mediumCommon Mistakes
- Cross multiplying incorrectly
- Setting up proportion backwards
Why This Formula Matters
Proportions are used in scaling, maps, recipes, unit conversion, and geometric similarity problems.
Frequently Asked Questions
What is the Proportions formula?
An equation stating that two ratios are equal, used to find an unknown when three of the four values are known.
How do you use the Proportions formula?
If 2 candies cost 1, then 4 candies cost 2—same proportion.
What do the symbols mean in the Proportions formula?
\frac{a}{b} = \frac{c}{d} states two ratios are equal; cross-multiplication gives ad = bc
Why is the Proportions formula important in Math?
Proportions are used in scaling, maps, recipes, unit conversion, and geometric similarity problems.
What do students get wrong about Proportions?
Setting up the proportion so matching units are in the same position (both in numerator or both in denominator).
What should I learn before the Proportions formula?
Before studying the Proportions formula, you should understand: ratios, equations.