1. Multiply 3-Digit and 4-Digit Numbers with Regrouping
Go Math!
Chapter 2
Lesson 2.11
Multiply 3-Digit and 4-Digit Numbers with Regrouping
Materials needed:
-dry erase boards, markers, and erasers
-Lesson 2.11 classwork
-Lesson 2.11 classwork riddles
-Lesson 2.11 homework sheet (teacher created)

2. Multiply by 1-Digit Numbers
Last time, we learned a third strategy for multiplying by one digit.
We answered this big question…

3. How can you use regrouping to multiply by a 1-digit number?
Can someone remind us?
Regrouping is a short cut method. It lets me find my partial products and combine them together all at the same time.
All of the problems we solved last time had…

4. 39 39 39 x 8 8 8 31 2 7 …a 2-digit number times a 1-digit number.
Let’s solve this problem by regrouping.
What place do I start with?
What would I multiply first? * 8 x 9 ones.
How many ones would that be? I can show that by regrouping. 72 ones = * 7 tens, 2 ones.
What would I multiply next? * 8 x 3 tens
How many tens is that?
What do I do with the 7 tens from when I regrouped?
What would I get? *
Today, we’ll use the regrouping method to solve some bigger problems. Let’s take a look… 31 2

5. Mrs. Lim purchased 4 new digital cameras for the school
Mrs. Lim purchased 4 new digital cameras for the school. Each camera cost $295. How much money did Mrs. Lim spend?
Would someone like to read this problem for us?
What problem would I need to solve to find out how much money Mrs. Lim spent? *
Let’s solve this problem by regrouping…
4 x $295

6. 3 2
$295
295
295
295 x 4 4 4
What place would I have to start with?
What would I multiply to find how many ones there are? *
How would I write that? *
What would I multiply to find out how many tens there are? *
What do I do with the 2?
What do I multiply to find out how many hundreds there are? *
What do I do with the 3?
What do I still need in my answer? * comma
Since I was trying to find out how much Mrs. Lim spent, how shall I label my answer? *
Let’s do a few more together… , $ 11 8

7. A series of books has 7 volumes. Each volume has 837 pages
A series of books has 7 volumes. Each volume has 837 pages. How many pages are there in the series? 2 4
Can someone read this problem?
What problem would I have to solve? *
What would I multiply to find how many ones there are? *
What would I get? How would I write that? *
What would I multiply to find out how many tens there are? *
What do I do with the 4?
What do I multiply to find out how many hundreds there are? *
What do I do with the 2?
What would I get? *
What do I still need in my answer? * comma
How should I label my answer? *
837
837
837
837 x 7 7 7 , 9 58 5
pages

8. Luke has 6 boxes of baseball cards. Each box has 203 cards
Luke has 6 boxes of baseball cards. Each box has 203 cards. How many cards does Luke have? 1
203
203
203
203
Can someone read this problem?
What problem would I have to solve? *
What would I multiply to find how many ones there are? *
What would I get? How would I write that? *
What would I multiply to find out how many tens there are? *
What do I do with the 1?
What do I multiply to find out how many hundreds there are? *
What would I get? *
What do I still need in my answer? * comma
How should I label my answer? *
Let’s do one more together… x 6 6 6 , 12 1 8
cards

9. A freight company is shipping 3 boxes that weigh 128 pounds each
A freight company is shipping 3 boxes that weigh 128 pounds each. How much do the boxes weigh altogether? 2
128
Can someone read this problem?
What problem would I have to solve?
What would I multiply to find how many ones there are?
What do you get? How would I write that? *
What would I multiply to find out how many tens there are?
What do I do with the 2?
How would I write that? *
What do I multiply to find out how many hundreds there are? *
How should I label my answer? *
Now it’s… x 3 3 8 4
pounds

10. Your
Turn!
…your turn to solve some three digit problems with regrouping.
You will need your dry erase board, marker, and eraser.
Here is your first problem to solve…

11. 2 2
423 x 9
Find the product of these two numbers. * 38 , 7

12. 2 4
159 x 5
Find the product of these two numbers. * 7 9 5

13. 506 4 20 2 4 , x 2 Find the product of these two numbers. *
Now let’s solve some even bigger problems!
For the moment, set your board to the side.
We’ll do a few together first… 20 2 4 ,

14. A band performed 3 sold out shows
A band performed 3 sold out shows. All 2,428 seats were filled for each show. How many fans saw the 3 shows?
Can someone read this problem?
What problem would I need to solve for this one? *
Let’s solve this problem with regrouping…
3 x 2,428

15. 1 2
2,428
2,428
2,428
2,428
2,428 3 3
What place will I need to start with?
What should I multiply to find out how many ones there are? *
What will I get? How would I write that answer? *
What should I multiply next? *
What else do I need in my answer? *
So 7,284 fans saw the three shows.
Let’s try another one… x 7 2 8 4 ,

16. The principal at Smithfield Elementary ordered 2 new sets of playground equipment for his school. Each set cost $6,753. What was the total cost of the new equipment?
Take a look at this problem. Can someone read it?
What problem would I need to solve for this one? *
2 x $6,753

17. 1 1
$6,753
$6,753
$6,753
$6,753
$6,753 2 2
What place will I need to start with?
What should I multiply to find out how many ones there are? *
What will I get? How would I write that answer? *
What should I multiply next? *
What else do I need in my answer? (*comma, *$)
So the principal spent $13,506.
Now it’s… x $ 13 , 5 6

18. Your Turn! …your turn to solve some problems with 4 digits.
You will need your dry erase board, marker, and eraser once again.
Here is your first problem to solve…

19. 5 3
6,095 6 x
Solve this problem!
What is your product? *
36, 5 7

20. 2
$4,328 3 x
Solve this problem!
What is your product? * $ 12 , 9 8 4

21. 4 2 3
1,957 5 x
Solve this problem!
What is your product? * 9 , 7 8 5

22. 1 2 3
$3,469 4 x
Solve this problem!
What is your product? *
Now let’s put our boards, markers, and erasers away and see if we can use what we learned to go deeper and solve some word problems.
Our book doesn’t give us much space to solve problems, so I typed the problems onto a new sheet of paper.
(pass out classwork sheet) $ , 13 8 7 6

23. (solve on screen while kids do on paper)

24. (solve on screen while kids do on paper)
Put this in the green section of your binder.
I have two new riddles for you to use to practice multiplying by regrouping.
(pass out riddles)
Before you may work on them, you need to first correct hw mistakes. Here are your…

25. Things to do: Correct all homework mistakes with RED
pencil. Do NOT erase or write on top of
answers!
…things to do (click to show each item).
Put your corrected homework sheets in the blue bin.
Complete the riddle sheets.