# Lesson 12

## Warm-up: Exploración de estimación: Llenémoslo (10 minutes)

### Narrative

The purpose of this Estimation Exploration is to practice the skill of making a reasonable estimate. Students consider how the placement of the first 2 squares can help them think about the total number of squares needed to fill the rectangle (MP7). These understandings will be helpful later when students will need to partition rectangles into equal-size squares.

### Launch

• Groups of 2
• Display the image.
• “¿Con cuántos cuadrados pequeños se llenaría el rectángulo?” // “How many little squares would fill the rectangle?”
• “¿Qué estimación sería muy alta?, ¿muy baja?, ¿razonable?” // “What is an estimate that’s too high?” “Too low?” “About right?”
• 1 minute: quiet think time

### Activity

• “Discutan con su compañero lo que pensaron” // “Discuss your thinking with your partner.”
• 1 minute: partner discussion
• Record responses.
• Draw equal-size squares to show:
• “¿Quieren reconsiderar lo que pensaron antes?” // “Would you like to revise your thinking?”
• 1 minute: quiet think time
• Share responses.

### Student Facing

Escribe una estimación que sea:

muy baja razonable muy alta
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### Activity Synthesis

• “¿Cómo les ayudó la segunda imagen a reconsiderar lo que habían pensado?” // “How did the second image help you revise your thinking?”
• Consider asking, “¿Cómo supieron que 11 no era una estimación razonable?” // “How could you tell that 11 would not be a reasonable estimate?” (The bottom row already has 4, so the 2 bottom rows will have 10. It has to be more than 11 because there is another row to fill.)

### Narrative

The purpose of this activity is for students to partition rectangles to create rows and columns of equal-size squares. In the launch, students build an array with tiles and then represent it on a rectangle with tick marks as guidance. They will partition rectangles without tick marks in the next activity.

MLR2 Collect and Display. Synthesis: Direct attention to words collected and displayed from the previous lessons. Include the word “partition.” Invite students to borrow language from the display as needed, and update it throughout the lesson.

### Required Materials

Materials to Gather

### Launch

• Groups of 2
• Give students rulers and inch tiles.

### Activity

• “Usen 8 fichas para hacer un rectángulo. Sus fichas deben estar organizadas en 2 filas” // “Use 8 tiles to make a rectangle. Your tiles should be in 2 rows.”
• 1 minute: independent work time
• “Ahora dibujen líneas en el rectángulo para mostrar los cuadrados de igual tamaño. Debe haber el mismo número de cuadrados que hay en el rectángulo que hicieron con las fichas. Usen una regla si les ayuda” // “Now, draw lines in the rectangle to show the squares. It should have the same number of equal-size squares as the rectangle you made out of tiles. You may use a ruler if it helps you.”
• 1 minute: independent work time
• “Van a dibujar líneas para partir 2 rectángulos más en cuadrados de igual tamaño. Si les ayuda, usen las fichas para construirlos primero” // “You will draw lines to partition 2 more rectangles into equal-size squares. You can also use the tiles to build it first, if that helps.”
• 10 minutes: independent work time

### Student Facing

1. Construye un rectángulo con 8 fichas organizadas en 2 filas. Parte el rectángulo usando una regla para que corresponda al rectángulo que hiciste.

2. Usa una regla para partir el rectángulo. Usa las marcas como guía.

2. ¿Cuántas columnas hiciste?
3. Escribe 2 ecuaciones que representen el número total de cuadrados de igual tamaño.
3. Usa una regla para partir el rectángulo. Usa las marcas como guía.

2. ¿Cuántas columnas hiciste?
3. Escribe 2 ecuaciones para representar el número total de cuadrados de igual tamaño.

### Student Response

If students create equations that match the total number of squares, but do not represent the sum of squares in each row or the sum of squares in each column, consider asking:

• “¿Cómo le corresponde tu ecuación al arreglo?” // “How does your equation match the array?”
• “¿Puedes escribir una ecuación que tenga sumandos iguales y que muestre la suma de cada fila o de cada columna?” // “Can you write an equation with equal addends that shows the sum of each row or column?”

### Activity Synthesis

• Invite 12 students to share their rectangles and equations for their rectangle with 3 rows and 5 columns. ($$3 + 3 + 3 + 3 + 3 = 15$$ or $$5 + 5 + 5 = 15$$)
• Draw a rectangle and partition to show:
• “¿En qué se diferencia esta partición de las que hicimos en la actividad?” // “How is this partition different from what we did in this activity?” (The squares aren’t the same size and the last column has 4 not 3.)

## Activity 2: Partamos rectángulos (20 minutes)

### Narrative

The purpose of this activity is for students to partition rectangles into rows and columns of equal-size squares. They use tiles to help them see how to draw lines to partition the rectangles. Although it is important for students to use what they know about the structure of arrays and composing rectangles from squares to partition the rectangles (MP7), it is not necessary that students’ drawings are perfect. As long as it is clear that the student intended for the squares to be equal in size and they can articulate their reasoning. If their squares are significantly different or result in more squares in one column or row than another, offer a ruler and consider having students trace tiles for practice or guidance.

Action and Expression: Develop Expression and Communication. Give students access to 1-inch grid paper to get their thinking started, and create an array with the inch tiles. Have students transfer what they made on the grid paper to the open rectangles given. The concrete image transferred to the more abstract image may help some students visually.
Supports accessibility for: Visual-Spatial Processing, Organization

### Required Materials

Materials to Gather

### Launch

• Groups of 2
• Give students rulers and inch tiles.

### Activity

• “Van a partir rectángulos. En el primer caso, hagan juntos un rectángulo usando fichas para planear su trabajo. Luego, partan uno de los rectángulos para que corresponda al rectángulo que hicieron” //  “You will be partitioning rectangles. For the first one, work with a partner to make a rectangle using tiles to help you plan, and then partition one of the rectangles to match.”
• 5 minutes: partner work time
• Monitor for a group who used each of the rectangles.
• Selected groups share.
• “¿Cómo decidieron cuál de los rectángulos dibujados usar para representar el rectángulo que hicieron con fichas?” // “How did you decide which drawn rectangle to use to represent your tile rectangle?” (Our rectangle had 2 tiles in each row so we used the taller rectangle.)
• “¿Podrían haber usado el otro rectángulo?” // “Could you have used the other rectangle?” (No, because the squares wouldn’t be the same size.)
• 30 seconds: quiet think time
• 1 minute: partner discussion
• Share responses.
• “Individualmente, partan los siguientes 2 rectángulos. Recuerden que todos los cuadrados deben ser del mismo tamaño. Cuando terminen, comparen sus rectángulos con los de su compañero” // “For the next 2 rectangles, work on your own to partition them. Remember that all the squares should be the same size. After you are done, compare with your partner.”
• 6 minutes: independent work time
• Monitor for students who have a solid strategy for making equal-size squares. Choose at least 1 student who thought about the number of squares first and 1 who drew the lines first and then counted the squares.

### Student Facing

1. Usa 12 fichas para hacer un rectángulo. Parte uno de estos rectángulos en cuadrados de igual tamaño para que corresponda al rectángulo que hiciste con las fichas.

### Activity Synthesis

• Invite previously identified students to share how they partitioned their rectangles.
• “¿Qué estrategias usaron para hacer todos sus cuadrados del mismo tamaño?” // “What strategies did you use for making your squares all the same size?” (I knew I wanted _____ squares, so I did _____ lines across and down. I started by making my rows, then made the lines for the columns, and then saw how many squares it made.)

## Lesson Synthesis

### Lesson Synthesis

Display a variety of arrays and rectangles from the unit, such as:

“En esta unidad aprendieron sobre números pares e impares y sobre diferentes tipos de arreglos. Examinen estas imágenes y piensen en 1 cosa que pueden decir sobre cada una. ¿En qué cosas se parecen? ¿En qué cosas son diferentes?” // “In this unit you learned about even and odd numbers and different types of arrays. Looking at these images, think about 1 thing you could say about each one. What are some things that are the same or different?”

Share and record responses.

$$4 + 4 + 4 + 4 + 4 = 20$$       o       $$5 + 5 + 5 + 5 = 20$$