Addition and Subtraction with Regrouping
Once children show an good understanding of place-value with tens and ones, introduce place-value with hundreds, tens, and ones.
Materials: place-value blocks, hundreds place-value mat
Preparation: Copy a hundreds mat for each child.
Prerequisite Skills and Concepts: Children should know place-value with tens and ones.
- Say: We have been working on place-value with 2-digit numbers. Today we are going to work with 3-digit numbers.
You will be using a new model to show your numbers.
- Introduce the ones, tens, and hundreds place-value blocks. Allow time for children to line up and compare ten ones to one ten block, and ten tens to a hundred block. Have children place the blocks in the correct position on their place-value mat.
- Say: I have ten ones. I want to trade them for another block that has the same value. Who will trade with me?
Have a volunteer show how you can trade ten ones for one ten. Repeat using ten tens and a hundred block. Then demonstrate trading 20 ones for 2 tens or 20 tens for 2 hundreds.
- Ask: If you have the number 162, how many hundreds, tens, and ones will you place on your mat?
Allow time for children to place their blocks, repeating the number as necessary. Children should place 1 hundred block, 6 tens blocks, and 2 ones blocks in the appropriate sections of their mat.
- Repeat the activity until the children place the blocks correctly and with ease.
- Say: Now we are going to try another number. It is 205.
- Ask: How many hundreds are there? (2)
How many tens? (0)
How many ones? (5)
- Ask: Are there blocks in every section of your mat?
Children should say that there are no blocks in the tens section.
- Ask: How will we write the number?
Lead children to express that they must write a zero when there are no blocks.
- Continue by challenging children to show numbers on their mats when you give the digits out of order. For example, say, I have 2 tens, 3 hundreds, and 6 ones. What number is that? I have no hundreds, 7 ones, and 3 tens. What number is that? This will make children pay careful attention to the place-value words.
Wrap-Up and Assessment Hints
place-value needs lots of practice. Reinforce the vocabulary. Remind children that it is very important to listen and write a number carefully; that the numbers should be in order and that the numbers should be in the correct position. As you assess each child, check the placement of their written numbers.
Addition and Subtraction with Regrouping:
Commutative and Associative Properties: