2 Develop the Concept: Interactive
10–15 min
Overview
Interactive Learning
In this activity, children will use place-value blocks to add three-digit
numbers.
Essential
Question
How can you model and record adding 2 three-digit numbers?
Materials
Place-Value Mat B (Teaching Tool 8, 1 per pair), hundreds flats (5 per pair),
tens rods (20 per pair), unit cubes (20 per pair)
Set the Purpose You know how to add two-digit numbers with and
without regrouping. Today you will learn how to add three-digit numbers
with and without regrouping.
Connect You have learned how to regroup 10 ones as 1 ten when adding
two-digit numbers. On the board, write 65 ⫹ 86 in vertical form. What is
the sum? [151] Did you have to regroup? Explain. [Yes; I had to regroup
10 ones as 1 ten when I added the ones.]
Have children work in pairs. On the board, write 246 ⫹ 371 in vertical
form. Work with your partner to find the sum. Use your place-value
blocks to help you. What is the sum? Do you have to regroup? Allow
time for children to work and to discuss their findings.
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Write the following addition exercises on the board in vertical form:
146 ⫹ 321, 184 ⫹ 375, 264 ⫹ 123, 277 ⫹ 165, 125 ⫹ 391,
and 189 ⫹ 248. Then direct children’s attention to Teaching Tool
8. You will use your place-value chart and models to help you add.
Work with your partner to find each sum. Record the answers in
Items 1–6 on page 559. [467; 559; 387; 442; 516; 437] After
children have completed the page, discuss if and how children
regrouped for each item.
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Model finding the sum with the class. Model each number with your
place-value blocks. What do you add first? [The ones] Do you have to
regroup? How do you know? [No; 6 plus 1 is 7, which is less than
1 ten.] Now you can add the tens. Do you have to regroup? How do
you know? [Yes; 4 tens plus 7 tens is 11 tens, or 110, which is more
than 1 hundred.] How can you regroup 10 tens rods? [You can trade
10 tens rods for one hundreds flat.] Now add the hundreds. How
many hundreds are there? [6 hundreds; 2 hundreds plus 3 hundreds
plus the regrouped 1 hundred.] What is the sum? [617]
© Pearson
Model/
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eTools Place-Value Blocks
www.pearsonsuccessnet.com
Models for Adding with Three-Digit Numbers 559
28273_559a-562b_PDF.indd 559
6/27/07 1:17:39 PM