Advanced Topics
In a nutshell: You can solve for unknowns in proportions using cross-multiplication.
## Steps to Solve Ratio and Proportion Problems
1. Write the ratios as fractions.
2. Set up the proportion.
3. Use cross-multiplication to find the missing value.
4. Check your answer by plugging it back in.
## Tips for Solving Problems
- Always simplify ratios first!
- Label your quantities to avoid confusion.
- Practice makes perfect—draw pictures or use tables for tricky questions.
## Example with Formula
If \( \frac{a}{b} = \frac{c}{x} \), then \( x = \frac{b \times c}{a} \).
x = \frac{b \times c}{a}
Examples
- If 4 pens cost $12, how much do 7 pens cost? Set up 4/12 = 7/x and solve for x.
- A model car is built at a 1:24 scale. If the real car is 12 feet long, the model is 0.5 feet (6 inches).
Key terms
- Cross-multiplication
- A method for solving proportions by multiplying across the equals sign.