standard_description: Add and subtract fractions with unlike denominators (including mixed numbers) by replacing given fractions with equivalent fractions in such a way as to produce an equivalent sum or difference of fractions with like denominators. For example, 2/3 + 5/4 = 8/12 + 15/12 = 23/12. (In general, a/b + c/d = (ad + bc)/bd.)
problem_activity: Narrative
The purpose of this activity is for students to create a connecting cube tower that is the same length as a given image. In the activity synthesis, students transition from describing the length of an object by comparing it to another object ("The earthworm is the same length as a tower of 8 cubes.") to describing the length of an object as a measurement ("The earthworm is 8 cubes long.").
Required Materials
Materials to Gather
Connecting cubes
Materials to Copy
Lengths of Creepy, Crawly Things
Launch
Groups of 2
Give each student connecting cubes and a copy of the blackline master.
Activity
“We just saw a picture that showed a pencil that was the same length as the purple tower. Use connecting cubes to build a tower that is the same length as each creepy, crawly thing.”
10 minutes: partner work time
Monitor for students who carefully line up the cubes with the endpoints of the images.
Student Response
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Activity Synthesis
Invite previously identified students to share.
Display the image of the caterpillar.
“How did you measure the caterpillar?” (I lined the first cube up with the end of the caterpillar. Then I added cubes until I got all the way to the other end of the caterpillar.)
“Since the tower of 4 cubes is the same length as the caterpillar and each cube has the same length, we can say the caterpillar is 4 cubes long.”
For each animal, invite students to say, “The ______ is ___ cubes long.”


aligns: no