A ratio compares two quantities. We write ratios in three ways:
Example: If there are 3 apples and 4 oranges, the ratio of apples to oranges is 3:4.
Write the ratio 5 to 8 in two other ways.
In a class, there are 12 boys and 15 girls. What is the ratio of boys to girls?
A recipe calls for 2 cups of flour and 3 cups of sugar. What is the ratio of flour to sugar?
If the ratio of red marbles to blue marbles is 4:7, and there are 20 red marbles, how many blue marbles are there?
A school has 240 students. The ratio of 6th graders to total students is 2:5. How many 6th graders are there?
Calculate: 3/4 + 2/3 = ?
Create your own real-world problem using the ratio 3:5. Show how to solve it.
If 3/4 = 0.75, what decimal equals 3/5?
Answer: 5:8 or 5/8
Three ways to write ratios: "to", colon, fraction
Answer: 12:15 or 4:5 (simplified)
Boys to girls = 12 to 15. We can simplify by dividing both by 3.
Answer: 2:3
Flour to sugar = 2 cups to 3 cups = 2:3
Answer: 35 blue marbles
If 4 red = 20, then 1 part = 5. So 7 blue parts = 7 × 5 = 35
Answer: 96 students
2:5 means 2 out of 5. (2/5) × 240 = 96 6th graders
Answer: 17/12 or 1 5/12
Find common denominator 12: 9/12 + 8/12 = 17/12
Answer: Varies (sample provided)
Example: "If John has 3 red pens and 5 blue pens, what is the ratio?"
Answer: 0.6
3 ÷ 5 = 0.6 (this previews next week's topic: decimals)