Adding it All Up
Students will be able to add a one-digit number to a two-digit number.
Introduction (5 minutes)
- Ask two volunteers to come to the front of the classroom.
- Give one student a two-digit number. Give the other student a one digit number. Instruct the students to use base-ten blocks to add their numbers together.
- Have the rest of the class use base-ten blocks to model the addition problem at their desks.
- Ask students to share some information. Great questions include: What is the sum of your addition problem? What strategies did you use to find the sum?
- Tell students that today we're going to add two-digit numbers.
Explicit Instruction/Teacher Modeling (10 minutes)
- Write the following problem on the board: Tess raked 18 leaves on Monday. She raked 7 leaves on Friday. How many leaves did she rake in all?
- Ask students to read the problem aloud with you.
- Guide students in using base-ten blocks to show 7 and 18.
- Explain to students that when adding a two-digit number, add the ones first. Then add the tens.
- Ask students how many ones there are total.
- Show students how to make a group of 10 ones, by connecting ten cubes together. Instruct them to trade these ten blocks for 1 ten.
- Discuss the term regrouping. Define regrouping as the process of changing groups of ones into tens to make adding and subtracting easier.
- Once you've made a ten from the ones, count the number of ones that are leftover.
- Ask students how many tens and ones are there now.
- Have students write a number sentence to solve the problem.
- Repeat steps using two different numbers.
Guided Practice/Interactive Modeling (10 minutes)
- Write the following problems on the board:
27 33 19 24 + 7 + 8 + 3 + 5
- Give each student an index card or half-sheet of paper.
- Work through the steps together to complete the problems.
- Remind students that a number line can also be used to help add.
Independent Working Time (15 minutes)
- Have students complete the problems on the Addition sheet independently.
- Enrichment: Challenge advanced students to complete the problems without manipulatives.
- Support: Encourage struggling students to continue using manipulatives to add, or to draw a picture to demonstrate how they can regroup.
Assessment (5 minutes)
- Tell students to turn their index card or half-sheet over, to complete a problem on the back.
- Ask them to find the sum for 17 + 6, and draw or write to explain how they found it.
Review and Closing (5 minutes)
- Review effective strategies for adding one-digit and two-digit numbers, including the definition for regrouping.