Lesson 7Creating Double Number Line Diagrams

Learning Goal

Let’s draw double number line diagrams like a pro.

Learning Targets

  • I can create a double number line diagram and correctly place and label tick marks to represent equivalent ratios.

  • I can explain what the word “per” means.

Lesson Terms

  • double number line diagram
  • per

Warm Up: Ordering on a Number Line

Problem 1

  1. Locate and label the following numbers on the number line:

    A number line with 0 marked on the far left and 2 marked on the far right.

  2. Based on where you placed the numbers, locate and label four more fractions or decimals on the number line.

Activity 1: Just a Little Green

Problem 1

The other day, we made green water by mixing 5 ml of blue water with 15 ml of yellow water. We want to make a very small batch of the same shade of green water. We need to know how much yellow water to mix with only 1 ml of blue water.

  1. On the number line for blue water, label the four tick marks shown.

    • On the number line for yellow water, draw and label tick marks to show the amount of yellow water needed for each amount of blue water.

    "A double number line where the top number line is labeled "blue water, in milliliters" and the numbers 0, 5, and 10 are indicated. There are 4 evenly spaced tick marks between 0 and 5. The bottom number line is labeled "yellow water, in milliliters" and the numbers 0, 15, and 30 are indicated."

  2. How much yellow water should be used for 1 ml of blue water? Circle where you can see this on the double number line.

  3. How much yellow water should be used for 11 ml of blue water?

  4. How much yellow water should be used for 8 ml of blue water?

  5. Why is it useful to know how much yellow water should be used with 1 ml of blue water?

Activity 2: Art Paste on a Double Number Line

A recipe for art paste says “For every 2 pints of water, mix in 8 cups of flour.”

Problem 1

  1. Follow the instructions to draw a double number line diagram representing the recipe for art paste.

    • Use a ruler to draw two parallel lines.

    • Label the first line “pints of water.” Label the second line “cups of flour.”

    • Draw at least 6 equally spaced tick marks that line up on both lines.

    • Along the water line, label the tick marks with the amount of water in 0, 1, 2, 3, 4, and 5 batches of art paste.

    • Along the flour line, label the tick marks with the amount of flour in 0, 1, 2, 3, 4, and 5 batches of art paste.

  2. Compare your double number line diagram with your partner’s. Discuss your thinking. If needed, revise your diagram.

Problem 2

Next, use your double number line to answer these questions:

  1. How much flour should be used with 10 pints of water?

  2. How much water should be used with 24 cups of flour?

  3. How much flour per pint of water does this recipe use?

Are you ready for more?

Problem 1

A square with side of 10 units overlaps a square with side of 8 units in such a way that its corner is placed exactly at the center of the smaller square. As a result of the overlapping, the two sides of the large square intersect the two sides of the small square exactly at points and , as shown. The length of is 6 units.

A square with side of 10 units overlaps a square with side of 8 units in such a way that its corner B is placed exactly at the center of the smaller square.

What is the area of the overlapping region ?

Activity 3: Revisiting Tuna Casserole

Problem 1

The other day, we looked at a recipe for tuna casserole that called for 10 ounces of cream of chicken soup for every 3 cups of elbow-shaped pasta.

  1. Draw a double number line diagram that represents the amounts of soup and pasta in different-sized batches of this recipe.

  2. If you made a large amount of tuna casserole by mixing 40 ounces of soup with 15 cups of pasta, would it taste the same as the original recipe? Explain or show your reasoning.

  3. The original recipe called for 6 ounces of tuna for every 3 cups of pasta. Add a line to your diagram to represent the amount of tuna in different batches of casserole.

  4. How many ounces of soup should you mix with 30 ounces of tuna to make a casserole that tastes the same as the original recipe?

Lesson Summary

Here are some guidelines to keep in mind when drawing a double number line diagram:

  • The two parallel lines should have labels that describe what the numbers represent.

  • The tick marks and numbers should be spaced at equal intervals.

  • Numbers that line up vertically make equivalent ratios.

For example, the ratio of the number of eggs to cups of milk in a recipe is . Here is a double number line that represents the situation:

a double number line for eggs: 0, 4, 8, 12, 16, 20 and cups of milk: 0, 1, 2, 3, 4, 5. The pairs $4:1$ and $8:2$ are circled.

We can also say that this recipe uses “4 eggs per cup of milk” because the word per means “for each.”