Math
Solving proportions.
Definition
Finding a missing value in a proportion (an equation stating that two ratios are equal). The main technique is cross-multiplication: if a/b = c/d, then ad = bc.
How it works · 4 phases
Step by step.
- Set up the proportion with the unknown variable.
- Cross-multiply to eliminate the fractions.
- Solve the resulting equation for the variable.
- Check the answer by substituting back into the original proportion.
Examples
Real-world.
- 1 3/4 = x/20 → 4x = 60 → x = 15
- 2 If a recipe for 4 servings needs 6 cups of flour, then 10 servings need x: 6/4 = x/10 → x = 15 cups
Key Fact
a/b = c/d → ad = bc