Lesson 9 A Sum of Equal Addends

    • Let’s match expressions with arrays.

Warm-up Estimation Exploration: How Many Waffles?

How many waffles are on the tray?

Waffles.
Tray of waffles.

Record an estimate that is:

too low

about right

too high

Activity 1 Sums of Rows and Sums of Columns

Mai and Diego represented the same array with different expressions.

Array. 6 rows of 2. 6 yellow, 6 red.

Diego’s expression

Mai’s expression

Who do you agree with?

Show your thinking using diagrams, symbols, or other representations.

Activity 2 Card Sort: Arrays and Expressions

Your teacher will give you a set of cards that show arrays, expressions and a total number. Find the cards that match.

Activity 3 Add It All Up

Problem 1

Array. 3 rows of 4. 6 red, 6 yellow.

  1. How many counters are there in all?

  2. Explain how you found the total number of counters.

  3. Circle 2 expressions that represent the array.

Problem 2

Array. 2 rows of 7. 8 yellow, 6 red.

  1. How many counters are there in all?

  2. Explain how you found the total number of counters.

  3. Circle 2 expressions that represent the array.

Practice Problem

Problem 1

  1. Circle the 2 expressions that represent the array.

    Array. 7 rows of 2. 7 red, 7 yellow.

  2. How many counters are there in the array?