Lesson 11 How Did You Do That?

    • Let’s add two-digit numbers and make sense of equations.

Warm-up True or False: Add to a Two-digit Number

Decide if each statement is true or false. Be prepared to explain your reasoning.

Activity 1 How Much Litter?

Kids picking up litter in a park.

Mai and her classmates volunteer to clean up the local park.
They pick up 37 plastic bottles and 25 paper wrappers.
How many pieces of litter did they pick up all together?

Jada, Kiran, and Tyler find the value of to find out how many pieces of litter Mai’s class picked up.

  1. Jada’s way:



    Base ten drawing. 3 tens and 2 tens, circled, labeled 50. 12 ones. Made of 10 ones, circled and labeled. Below 2 ones, labeled. 

  2. Kiran’s way:


    Base ten drawing. Top row, 3 tens, 10 ones, circled and labeled 10. Below, labeled 40. 2 ones, not circled. Below labeled 42. 2 tens. Below, 62.

  3. Tyler’s way:


Activity 2 It’s Your Turn to Add

Girl with thought cloud, 23 plus 68.

  1. Find the value of .
    Show your thinking using drawings, numbers, or words.

  2. If you have time… Think about a math story this expression could represent.
    Share your stories with a partner.

Practice Problem

Problem 1

Use your favorite method to find the value of .
Why do you like the method you chose?