Learn it
A ratio compares two quantities. If a bag has 3 red and 5 blue marbles, the ratio of red to blue is 3 to 5, written 3:5 or 3/5.
Order matters: blue to red is 5:3. A part-to-whole ratio compares a part to the total: red to all marbles is 3:8.
Equivalent ratios come from multiplying or dividing both parts by the same number: 3:5 = 6:10 = 9:15. A ratio table helps you list them.
Worked examples
Example 1
A recipe uses 2 cups of flour for every 3 eggs. How much flour for 12 eggs?
- Eggs went from 3 to 12, which is × 4
- Flour: 2 × 4 = 8
Answer: 8 cups
Example 2
A class has 12 girls and 18 boys. Write the ratio of girls to boys in simplest form.
- 12:18
- Divide both by 6
Answer: 2:3
Practice
Try these on paper first, then check your work.
- Ratio of 4 cats to 10 dogs, simplest form
- Complete 5:2 = 20:?
- Part-to-whole: 7 wins, 3 losses. Wins to games?
- Is 4:6 equivalent to 10:15?
Show the answer key
- 2:5
- 8
- 7:10
- Yes, both are 2:3