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 apply what they learned in earlier lessons to represent a division situation. During the synthesis, students connect what they know about division to multiplication when they see that the situation of 2 people equally sharing the distance in a 3 mile race can also be described as each person running one-half of the three mile race. Students connect the language they used to describe the situation to multiplication and division expressions. This relationship between multiplication and division is the focus of the next several lessons.
This activity uses
MLR2 Collect and Display.
Advances: Conversing, Reading, Writing.
Launch
Display the image from the student workbook.
“Tell a story about this image to your partner.”
“This image shows two children who are running in a relay race. They are on the same team. They each have to run the same distance. The boy holding the baton is finishing his turn. When he hands the baton to his teammate, his teammate will take her turn.”
Activity
Groups of 2
2 minutes: independent think time
5–8 minutes: partner work time
MLR2 Collect and Display
Circulate, listen for and collect the language students use to describe how to represent the situation and how far each person ran.
Listen for:
3 miles divided into 2 parts
half of 3 miles
one and one half miles
three halves
Record students’ words and phrases on a visual display and update it throughout the lesson.
Student Facing
[IMG]
Lin and Han ran a 3 mile relay race as a team. They each ran the same distance. Draw a diagram to represent the situation.
Take turns describing to your partner how your diagrams represent the situation.
How far did each person run?
Student Response
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Activity Synthesis
“These are the words and phrases that you used to describe the situation. Are there any other words or phrases that are important to include on our display?”
As students share responses, update the display, by adding (or replacing) language, diagrams, or annotations.
Display:
\(3 \div 2\)
,
\(1\frac{1}{2}\)
,
\(\frac{3}{2}\)
, and
\(3\times \frac{1}{2}\)
“How does each of these expressions represent the situation?” (3 miles was divided into 2 equal parts, each person ran
\(1\frac{1}{2}\)
miles or
\(\frac{3}{2}\)
miles which can be thought of as
\(3\times \frac{1}{2}\)
.
Consider giving students time to record their answers in their journal.
Display: “one half of 3 miles”
“This is another way to describe how far each person ran.”
Display:
\(\frac{1}{2}\times3\)
“We can also use this multiplication expression to represent one-half of 3.”
“In the next activity, you will describe how different diagrams represent each of these expressions.”


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