The purpose of this Number Talk is for students to demonstrate strategies and understandings they have for multiplying a fraction by a whole number. These understandings help students develop fluency and will be helpful later in the lesson when students explore the relationship between multiplication and division.
Launch
Display one expression.
“Hagan una señal cuando tengan una respuesta y puedan explicar cómo la obtuvieron” // “Give me a signal when you have an answer and can explain how you got it.”
1 minute: quiet think time
Activity
Record answers and strategy.
Keep expressions and work displayed.
Repeat with each expression.
Encuentra mentalmente el valor de cada expresión.
Student Response
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Advancing Student Thinking
Activity Synthesis
Display equation:
“¿Cómo sabemos que esto es cierto?” // “How do we know this is true?” (They are both equal to or 7 is so is ).
Activity 1
Standards Alignment
Building On
Addressing
5.NF.B.3
Interpret a fraction as division of the numerator by the denominator . Solve word problems involving division of whole numbers leading to answers in the form of fractions or mixed numbers, e.g., by using visual fraction models or equations to represent the problem. For example, interpret as the result of dividing by , noting that multiplied by equals , and that when wholes are shared equally among people each person has a share of size . If people want to share a -pound sack of rice equally by weight, how many pounds of rice should each person get? Between what two whole numbers does your answer lie?
The purpose of this activity is for students to apply what they learned in earlier lessons to represent a division situation. During the Activity Synthesis, students connect what they know about division to multiplication. Students 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
Groups of 2
Display the image from the student book.
“Cuéntenle a su compañero una historia sobre esta imagen” // “Tell a story about this image to your partner.”
“En esta imagen se ven dos niños corriendo en una carrera de relevos. Están en el mismo equipo y ambos deben correr la misma distancia. El niño que lleva el testigo está terminando su turno. Cuando le pase el testigo a su compañera de equipo, ella tomará su turno” // “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
2 minutes: independent think time
5–8 minutes: partner work time
MLR2 Collect and Display
Circulate to 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.
Lin y Han corren, en equipo, una carrera de relevos de 3 millas. Ambos corren la misma distancia. Dibuja un diagrama que represente la situación.
Por turnos, descríbanle a su compañero de qué manera sus diagramas representan la situación.
¿Qué distancia corrió cada persona?
Student Response
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Advancing Student Thinking
Activity Synthesis
“Estas son las palabras y las frases que ustedes usaron para describir la situación. ¿Qué otras palabras o frases importantes deberíamos incluir en nuestra presentación?” // “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: , , , and
“¿De qué manera cada una de estas expresiones representa la situación?” // “How does each of these expressions represent the situation?” (3 miles was divided into 2 equal parts. Each person ran miles or miles which can be thought of as .)
Consider giving students time to record their answers in their journal.
Display: “la mitad de 3 millas” // “one-half of 3 miles”
“Esta es otra forma de describir cuánto corrió cada persona” // “This is another way to describe how far each person ran.”
Display:
“También podemos usar esta expresión de multiplicación para representar la mitad de 3” // “We can also use this multiplication expression to represent one-half of 3.”
“En la siguiente actividad, van a describir de qué manera distintos diagramas representan estas expresiones” // “In the next activity, you will describe how different diagrams represent each of these expressions.”
Activity 2
Standards Alignment
Building On
Addressing
5.NF.B.3
Interpret a fraction as division of the numerator by the denominator . Solve word problems involving division of whole numbers leading to answers in the form of fractions or mixed numbers, e.g., by using visual fraction models or equations to represent the problem. For example, interpret as the result of dividing by , noting that multiplied by equals , and that when wholes are shared equally among people each person has a share of size . If people want to share a -pound sack of rice equally by weight, how many pounds of rice should each person get? Between what two whole numbers does your answer lie?
The purpose of this activity is for students to build on the previous activity to interpret diagrams as representing different expressions. Both diagrams in the activity represent solutions to the running situation in the previous activity. In this activity, the diagrams are interpreted without the running context. As students use the diagrams to interpret expressions, they begin to see relationships between the expressions , , , , and . In this activity, students make sense of different ways to interpret a given diagram and relate the operations of division and multiplication (MP7).
MLR1 Stronger and Clearer Each Time. Synthesis: Before the whole-class discussion, give students time to meet with 2–3 partners to share and get feedback on their response to “¿Cómo se representa cada expresión en los diagramas?” // “How is each expression represented in the diagrams?” Invite listeners to ask questions, to press for details and to suggest mathematical language. Give students 2–3 minutes to revise their written explanation based on the feedback they receive. Advances: Writing, Speaking, Listening
Launch
Groups of 2
Activity
5 minutes: independent work time
5–8 minutes: partner discussion
Monitor for students who choose different diagrams to represent the same expression.
Diagrama ADiagrama BEn cada caso, escoge un diagrama que creas que representa mejor la expresión. Describe de qué manera el diagrama que escogiste representa esa expresión. Explica tu razonamiento.
Activity Synthesis
“¿En qué se parecen los diagramas?” // “What is the same about the diagrams?” (They both show 3 rectangles that are divided into 2 equal pieces.)
“¿En qué son diferentes los diagramas?” // “What is different about the diagrams?” (The shaded pieces are next to each other in one of the diagrams.)
Ask previously selected students to share their explanations.
Display expression:
“¿Cuál diagrama escogieron para la expresión ? ¿Por qué?” // “Which diagram did you choose for the expression ? Why?” (I chose Diagram A because I see the 3 miles and the 2 equal parts. I chose Diagram B because I can see the 2 equal parts that make 3 miles and they make miles.)
Display expressions: , ,
“¿Cómo sabemos que todas las expresiones son iguales?” // “How do we know all the expressions are equal?” (The same diagram represents all of them. They all equal or .)
Lesson Synthesis
Record answers to the questions below for all to see and save responses to revisit during the Activity Synthesis of an upcoming lesson.
“¿Cuándo usamos la multiplicación hoy?” // “When did we use multiplication today?” (In the first activity, we found one half of three miles and we can show that with . The diagrams from the second activity represent and .)
“¿Cuándo usamos la división hoy?” // “When did we use division today?” (During the first activity, we divided 3 miles into 2 equal parts to figure out how far each person ran. The diagram from the second activity represents , and .)
“¿Qué aprendimos sobre la relación que hay entre la multiplicación y la división?” // “What did we learn about the relationship between multiplication and division?” (We can use both of them to solve and represent the same problem.)
“¿Qué se preguntan todavía sobre la relación entre la multiplicación y la división?” // “What do you still wonder about the relationship between multiplication and division?” (Can we always use multiplication or division to solve a division problem?)
Standards Alignment
Building On
4.NF.B.4
Apply and extend previous understandings of multiplication to multiply a fraction by a whole number.
Write simple expressions that record calculations with numbers, and interpret numerical expressions without evaluating them. For example, express the calculation “add and , then multiply by ” as . Recognize that is three times as large as , without having to calculate the indicated sum or product.