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Let's Jump to Add Two-Digit Numbers
Students will be able to add two-digit numbers using expanded form and a number line.
- Invite two student volunteers to go head to head and answer a place value question. Explain to the students that whoever answers the question correctly first stays standing and faces another student for the next question. Provide encouragement to students who answer the questions wrong by giving out high fives.
- Focus on past knowledge questions relating to identifying place values. Examples: "Tell me the value of 3 in 93 (3 ones). What number is in the tens place in 49 (4)? For 37, which number is greater, the digit in the tens place or the digit in the ones place (tens place)?"
- Say, “All those questions focused on place value. Now we will use our understanding of place value to add using a number line."
Explicit Instruction/Teacher modeling(10 minutes)
- Read the learning objective to the class.
- Provide examples of expanded form, which is when we expand the number to show the value of each digit (eg. 56 = 50 + 6).
- Give students an example of a number line, which is a line that has marked intervals. This is a tool we can use to perform operations in a visual way.
- Remind students that two-digit numbers are numbers that have a whole number in the ones and tens place.
- Explain to students that they will need to pay attention to place value as they add two-digit numbers in this lesson. Review the definition of place value as the value that each digit has in a number (eg. "In the number 56, the 5 is really 50 because it is 5 tens and the 6 is 6 ones.")
- Introduce the Add on Number Line Checklist that you have displayed, and discuss the elements with the students (talk over what strategies are used and highlight the key words).
- Provide a sample problem (80 + 13) and check off each step as you complete it.
- Model two more problems (75 + 23 and 89 + 10).
- Ask students to copy your work on their whiteboards as you complete the problems.
- Demonstrate how to add two-digit numbers on a number line when you have to carry (59 + 27). (Tip: You can show them how to add ten at a time or add to a multiple of ten, and then finish adding the expanded form values.)
Guided Practice(15 minutes)
- Say, “I’m having trouble coming up with all these number problems. Let’s just use this card deck and solve some more two-digit problems together.”
- Write on the board a two-digit addition equation with blanks (one blank space for each digit), and draw numbers from the deck of cards to create the two digits. (Tip: Drawing from the deck will help reinforce place value as you draw a number and ask students where to place the numbers.)
- Distribute some of the cards to each pair of students, and have them draw their own two-digit numbers.
- Instruct students by saying, “Okay, now you will draw your own digits and use the Add on Number Line Checklist to guide you as you solve two problems with your partner."
- Request that at least two students share their answer and their process.
- Have the students "take a stand" for the answers after each student has shared their problems and answers. The students will stand if they agree the problem is correct and sit if they think it is wrong. Choose a student that says the problem is wrong to explain their reasoning.
Independent working time(10 minutes)
- Explain: “Now that you have practiced adding two-digit numbers with me and your partner, you will do that same thing on your own.”
- Pass out a copy of the Faster, Faster: Two-Digit Addition #20 worksheet to each student.
- Remind students to continue to refer to the Add on Number Line Checklist as they work through the problems.
- Explain the directions and pass out additional scrap paper for students to draw the number lines.
- Break down expanded form to word form. For example, instead of 98 = 90 + 8, use 98 = 9 tens + 8 ones.
- Draw and label the number line for struggling students.
- Challenge students to draw the number lines themselves when they show understanding through reteaching.
- Use two-digit numbers that have no carrying involved (eg. 25 + 23, 51 + 32).
- Start with basic two-digit problems, and then transition to regrouping problems that bring students to 100. (eg. 87 + 13, 67 + 33, 49 +51)
- Provide the 2 Math Minutes: Addition worksheet to challenge students to perform the operation with speed and accuracy.
- Elevate student thinking by challenging them to create their own equations from word problems using the Number Line Math worksheet.
- Distribute scrap paper.
- Display the exit ticket problems on the board:
- 78 + 11 =
- a. 78 = _____ + ____
- b. Number Line
- c. The total amount is ____.
- d. Write a complete equation.
- 78 + 11 =
- Collect exit tickets to serve as a formative assessment of student understanding.
- Evaluate two-digit addition understanding based on student responses on the Faster, Faster: Two-Digit Addition #20 worksheet and exit ticket.
Review and closing(2 minutes)
- Review the student objective and ask students if they think they have met the objective. Require one or two students to defend their positions.
- Say, “Today we've jumped on a number line using the values from expanded form. Another way we can jump on a number line is counting by twos. Let's close out our lesson today by counting by twos up to 20.”
- Play the Counting by Twos video.