More Than Two Numbers
Lesson 4 of 8
Objective: The students will be able to find the sum of addition sentences with three addends.
This lesson begins with the students explaining to each other (turn and talk) what they know about addition problems. The hope is they would acknowledge that there are two addends, which when added together equal the sum.
I then ask the students to make a train of linking cubes, 4 with one color cube, and 5 of another color. Have them turn and talk about how they would demonstrate adding those trains.
Develop the Concept
I then ask the students to make a train of 4 with one color cube, 6 of another color, and 5 of another color.
Think, how can we add these numbers? What kind of number sentence would we need to make?
I tell the children that I am comfortable adding two numbers but when you put another number into the problem I get all nervous. Can you share any way that I can help make this problem easier and calm my nerves? Most of the time the students will tell me that I can look at it in pieces and simply add two of the numbers first and then add the third.
I write another problem on the board and have the students turn and talk about how they would solve it. After a brief chat, I demonstrate how to circle the first two numbers we choose to begin with, draw a caret over and write the addition problem for that number sentence and solve. Then I take that sum, write a new number sentence with the new addend and the remaining addend to solve the entire problem.
Now I have the students use their white boards to complete several more examples, spending time afterwards to discuss how each problem was solved. The sum of these examples will all be within 20. One thing to keep in mind when demonstrating addition is to show it both vertically, and horizontally.
Practice the Concept
Students work in partners to play the Group 'Em, Add 'Em Game. Each pair will need game papers (I make mine 2 sided, one per student) and three dice.
The first player rolls all three dice and uses those numbers to write a number sentence. They then solve each problem, using the method taught. They play until all problems have been completed. The students can compete, if you’d like, to see who rolls the number sentence with the greatest sum.
Have students come back together as a class. Encourage students to turn and talk about what they learned about adding three or more numbers. Have the students discuss any tricks they learned. How would you use this in the real world?