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Let's Build It! Two-Digit Addition
Students will be able to add two-digit numbers using both actual and written base-ten blocks.
- Practise counting by tens as a class. As you count, hold up the base-ten rods so that, at the end, you will be holding 10 rods to equal 100.
- Show on the board how adding 10 over and over is counting up and building bigger numbers.
- Call on students quickly and have them solve problems in which they add 10 every time (50 + 10, 30 + 10, 10 + 10).
- Say, “Base-ten blocks help us have a visual of what we are adding, especially when we are adding larger two-digit numbers.”
Explicit Instruction/Teacher modeling(10 minutes)
- Read the student objective and define the key words with the students—Two-digit numbers(one whole number in both the ones and tens place) and Bas- ten blocks(a manipulative used to teach maths).
- Use a Place value chart(a tool used to teach place value) and base-ten blocks to demonstrate 54 and 3. (Tip: Mention there are 10 of the ones (units) in a rod and show how ten ones adds up to one rod.)
- Write the numbers 54 and 3 on the board, and use five lines to represent five rods and three dots to represent the ones.
- Write 54 + 3 on the board, along with the base ten visual representation.
- Model adding the ones and then the tens on the board to get the total remaining two-digit number (57).
- Solve one more problem that requires the students to carry, or convert, 10 or more ones into a rod (26 + 4 or 39 +8).
- Require students to draw on their whiteboards the equation and base-ten blocks as you solve the problem on the board while asking questions (such as, “Should we keep all 12 ones as dots? Why should we make the 10 ones into a rod? How would we write the visual into equation form?").
- Say, “Now that I’ve shown you how to visually create two-digit numbers with base-ten blocks and add up two-digit numbers, we will practise some more together and in partners.”
Guided practise(15 minutes)
- Speed-practise drawing the numbers on the whiteboard and holding up their answers.
- Do this three times with the numbers 44, 16, and 8.
- Assign students a partner and two problems to solve together (65 + 20 and 33 + 9).
- Review partner answers with the class. With 33 + 9, monitor to make sure they were able to convert the 12 ones into another rod and two ones for a total answer of four rods and two ones.
Independent working time(10 minutes)
- Say, “Now you will show me how you can add two-digit numbers with base-ten visual models.”
- Pass out the Count and Add Blocks worksheet and explain the directions.
- Reinforce the use of the base-ten blocks in both written form and the actual blocks for assistance.
- Allow students to use base-ten blocks for all of the problems for tactile reinforcement. For example, they can use the base-ten blocks to create each of the two-digit numbers, and then have them draw the the lines and dots to represent the base-ten blocks.
- Provide two-digit numbers to add with more frequent carrying.
- Challenge students with two-digit addition with the Shopping with Daddy worksheet.
- Collect the Count and Add Blocks worksheet, and evaluate students’ understanding of place value, base ten-blocks, and adding two-digit numbers.
- Distribute the exit ticket and read the directions with the students.
- Monitor and assist students throughout the guided and independent practise.
Review and closing(2 minutes)
- Review the student objective, and ask students if they think they have met the objective.
- Say, “There are a lot of ways we can add two-digit numbers, and this is just one visual way that you can use in future addition and subtraction problems.”