1. Math 5 Multiplication: 2-digit x 2-digit
Instructor: Mrs. Tew Turner

2. In this lesson we will learn about Multiplication (2-digit x 2-digit).

3. Math Warm-up Round to the nearest dollar. $5.91 $17.03 $11.85 $0.97

4. Round to the nearest dollar.
Math Warm-up
Round to the nearest dollar.
$ $6.00
$ $17.00
$ $12.00
$ $1.00

5. In the last lesson you learned how to estimate to find the product of multiplication problems.
In this lesson we will answer the question:
How can you find the exact answer to multiplication problems?

6. Vocabulary
factors - numbers that are multiplied to get a product
product - the number that is the result of multiplying two or more factors
partial product - products found by breaking one of two factors into ones, tens, hundreds, and so on, to multiply each.

7. How do you multiply by 2-digit numbers?
Let's look at this problem:
The principal of a school is buying 3 computers at $900 each. She can pay $98 per month instead of paying for them at once. Will she have paid for the computers by the end of 12 months?

8. How do you multiply by 2-digit numbers?
Let's look at this problem:
The principal of a school is buying 3 computers at $900 each. She can pay $98 per month instead of paying for them at once. Will she have paid for the computers by the end of 12 months?
Let's underline the KEY QUESTION first.

9. How do you multiply by 2-digit numbers?
Let's look at this problem:
The principal of a school is buying 3 computers at $900 each. She can pay $98 per month instead of paying for them at once. Will she have paid for the computers by the end of 12 months?
Now let's circle the IMPORTANT NUMBERS to SOLVE the problem.

10. The principal of a school is buying 3 computers at $900 each
The principal of a school is buying 3 computers at $900 each. She can pay $98 per month instead of paying for them at once. Will she have paid for the computers by the end of 12 months?
Now let's circle the IMPORTANT NUMBERS to SOLVE the problem.
We need to MULTIPLY 3 x 900 to see what is the total cost for the computers.
This is easy, right? 3 x 9 = zeros = 2700.

11. The principal of a school is buying 3 computers at $900 each
The principal of a school is buying 3 computers at $900 each. She can pay $98 per month instead of paying for them at once. Will she have paid for the computers by the end of 12 months?
Can the computers be paid off in 12 months?
Multiply $98 x 12 = ? (Will it be enough?)
This will let us know if the principal can pay 2700 dollars in 12 months.

12. STEP 1: Multiply by the ONES place.
(partial product with ones factor) 98
x 12
196
2 x 8 ones = 16
Regroup 16 as 1 ten and 6 ones
2 x 9 tens = 18 tens or 1 hundred & 8 tens + 1 ten carried = 19 tens or 1 hundred 9 tens.

13. STEP 2: Multiply by the TENS place.
(partial product with tens only) 98
x 12
196
980
10 x 8 ones = 80 ones or 8 tens
10 x 9 tens = 90 tens or 9 hundred

14. STEP 3: Add the partial products.1 98
x 12
1196
+980
1176
Can the computers be paid off in 12 months?
(Will $1,176 be enough?)
Can the principal pay $2,700 dollars in 12 months?
NO, she will not be able to pay them off.

15. Check your answer with estimation!
x x 12
~1200
+980
1176
(Estimated answer is very close the exact answer and let's us know if our answer is reasonable.)

16. How do you multiply by 2-digit numbers?
REVIEW the STEPS
Step 1:
Multiply by the ONES place. Regroup if necessary.

17. How do you multiply by 2-digit numbers?
REVIEW the STEPS
Step 2:
Multiply by the TENS PLACE.
Regroup.

18. How do you multiply by 2-digit numbers?
REVIEW the STEPS
Step 3:
Add the PARTIAL PRODUCTS.
Easy as ....

19. Independent Practice
Find each product following the steps:
x x x x x16
Easy as ....

20. Estimate first to see what the answer will be closest to!
Independent Practice
Estimate first to see what the answer will be closest to!
x x x x x16
x x x 20 x x 20

21. Independent Practice How did you do? 1. 44 2. 26 3. 17 4. 35 5. 45
x x x x x16
1, ,

22. Quick Check In your Math Notebook
Writing to explain: How can finding the product of 5 x 700 help you check the product of 5 x 789?
Math Notebook

23. Quick Check In your Math Notebook Response Example
Writing to explain: How can finding the product of 5 x 700 help you check the product of 5 x 789?
5 x 700 = 3500
The real answer will be more since 700 is rounding DOWN. The EXACT answer will be MUCH MORE. This will not be the closest estimate.

24. Quick Check In your Math Notebook Response Example
Writing to explain: How can finding the product of 5 x 700 help you check the product of 5 x 789?
5 x 800 = 4000
The real answer will be less since 800 is rounding UP. The EXACT answer will be LESS. This will be the closest estimate.

25. Quick Check In your Math Notebook Response Example
Writing to explain: How can finding the product of 5 x 700 help you check the product of 5 x 789?
x 9 =
x x 80 =
3, x 700 = 3500
3945

26. Quick Check In your Math Notebook Response Example
Writing to explain: The estimate answer of 4,000 was a very close estimate!
x 9 =
x x 80 =
3, x 700 = 3500
3945

27. Good Work with this lesson.
Today you learned how to multiply 2 -digit by 2 digit Numbers!