The purpose of this Choral Count is to invite students to practice counting by 2 and 5 and notice patterns in each count. These understandings help students develop fluency and will be helpful later when students find factor pairs. In the Activity Synthesis, students are also invited to notice numbers that are in both counts and begin to reason why this may happen based on their emerging understanding of factors and multiples.

When students identify and predict common multiples for 2 and 5 based on the numbers recorded from the count and what they know about multiplication, they look for and express regularity in repeated reasoning (MP8).

This is the first time students experience the Choral Count routine in IM Grade 4. Students are familiar with this routine from a previous grade. However, they may benefit from a brief review of the steps involved.

• Select 1–2 patterns for each count to discuss. Consider asking:
  • “¿Alguien quiere compartir otra observación sobre por qué ocurre ese patrón aquí?” // “Does anyone want to add an observation on why that pattern is happening here?”
  • “¿Están de acuerdo o en desacuerdo? ¿Por qué?” // “Do you agree or disagree? Why?”
• “¿Cuáles números están en ambas listas? ¿Por qué creen que pasa eso?” // “What numbers are in both lists? Why do you think that happens?” (10, 20, and 30 are in both lists. It’s because they are multiples of both 2 and 5. 2 and 5 are both factors for each of those numbers.)
• “Si los conteos siguieran, ¿qué otros números verían que son múltiplos tanto de 2 como de 5?”//  “If the counts continue, what other numbers would you see that are multiples of both 2 and 5?” (I think 40 would be the next common multiple because the multiples are going up by 10. I think 100 would be a common multiple because and .)

The purpose of this activity is for students to learn about prime numbers and composite numbers. Students are given a set of cards with rectangles on them. They sort the rectangles by area and then attempt to draw an additional rectangle for each category. They notice that some areas can be represented by more than one rectangle and some areas can only be represented by one rectangle.

During the Activity Synthesis, highlight that the side lengths of each rectangle represent one factor pair (each pair of side lengths should be used only once), and that the area of each rectangle represents a multiple of each side length. Students learn that a number with only one factor pair—1 and the number itself—is a prime number, and a number with more than one factor pair is a composite number.

In this activity, students use the area of rectangles to find all factor pairs of a given whole number and decide if the number is prime or composite. The Activity Synthesis focuses on finding all possible rectangles for a given area as a strategy to find all the factor pairs of a number. Students may notice that they do not need to find all possible rectangles to determine whether a number is prime or composite.