Hop! Hop! Hop!: Strategic Number Lines
Use the number line strategy to solve three-digit addition problems.
- Lead the students in counting the three-digit number, 437, using base ten blocks.
- Demonstrate how the same number can be counted by creating a number line. (Start at 0 and count four hundreds, showing one “hop” for each 100 and marking the place for each hundred. Continue with the 3 tens and 7 ones.)
- Lead the students in counting the number using the number line.
- Tell the students that they will be learning how to add three-digit numbers using the number line strategy.
Explicit Instruction/Teacher modeling(5 minutes)
- Write the following problem on the board: 171 + 252.
- Using a whiteboard or interactive whiteboard, draw a long vertical line.
- Show the students how you can find the largest number. Circle that number and tell the students that this will be the starting number.
- Show the students how to label a point on the line with the starting number of 252.
- Demonstrate the process of labeling each part of the number, 171, with an “H” for hundreds, “T” for tens, and “O” for ones.
- Show the students how you can draw a curved line from the starting point to another point, labeling that +100 and representing a hop.
- Continue by demonstrating the tens and the ones.
- If you need a demonstration of this strategy in use you can find an example of this strategy in the following video: Adding 3 Digit Numbers Using a Number Line.
Guided Practice(10 minutes)
- Tell the students that they are going to get to practice timeline addition by using their bodies to hop and count.
- Lead the students outside to a large area of pavement or concrete with the sidewalk chalk, small whiteboard, and whiteboard marker. (As an alternative to the outside activity this can be adapted for use indoors. To do this activity indoors, use a long rope. Individual index cards can be used to place along the rope to designate adding hundreds, tens, and ones.)
- Tell the students that they will be using their bodies to hop and add numbers using a number line.
- Draw a long number line on the pavement.
- Invite students to make a semi-circle around the number line so that all students can see the number line.
- Write the problem, 425 + 224, on the whiteboard so that all the students can see it.
- Invite a student to participate in hopping along the line as the class practices the strategy. (Other students can hop in place as you count.)
- Ask the students to help identify the starting number and to help label the hundreds, tens, and ones places of the second number.
- Lead the students in adding the hundreds, tens, and ones to the number to get the answer, 649.
Independent working time(15 minutes)
- Divide the class into small groups of three or four students.
- Give each group a piece of sidewalk chalk, a whiteboard, and a whiteboard marker.
- Ask the students to complete the following problem using the chalk and the number line strategy: 523 + 129.
- Rotate around the area, checking students’ work.
- As students finish, give them additional practice problems: 264 + 478, 323 + 193, and 543 + 242
- Pre-teach adding numbers with four digits and challenge students to complete four-digit addition problems.
- Ask students to compare and contrast the number line strategy with other addition strategies.
- Provide examples with diagrams of hops drawn ahead of time.
- In place of using a rope and cards for an indoor activity, use the SMARTboard and have the students hop in place as they count.
- Invite the students to create digital diagrams of the number line counting using digital drawings. They can use a single line and curved lines to represent each hop.
- Distribute the worksheet, Hop to It.
- Ask students to complete the worksheet, showing how they used the number line strategy.
Review and closing(5 minutes)
- Invite the students to form a circle.
- Ask the students to share what made this strategy easier or more difficult than other strategies. When would this strategy be easiest to use? When would it be more difficult?