Math 5Multiplication: 2-digit x 2-

digit

Instructor: Mrs. Tew Turner

In this lesson we will learn about

Multiplication (2-digit x 2-digit).

Math Warm-up

Round to the nearest dollar.

a. $5.91b. $17.03c. $11.85d. $0.97

Math Warm-up

Round to the nearest dollar.

a. $5.91 $6.00b. $17.03 $17.00c. $11.85 $12.00d. $0.97 $1.00

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?

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

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?

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.

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.

How do you multiply by 2-digit numbers?

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 = 27 + 2 zeros = 2700.

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.

STEP 1: Multiply by the ONES place.(partial product with ones factor) 1

98x 12196

2 x 8 ones = 16 Regroup 16 as 1 ten and 6 ones2 x 9 tens = 18 tens or 1 hundred & 8 tens + 1 ten carried = 19 tens or 1 hundred 9 tens.

STEP 2: Multiply by the TENS place.(partial product with tens only)

1

98x 12196980

10 x 8 ones = 80 ones or 8 tens 10 x 9 tens = 90 tens or 9 hundred

STEP 3: Add the partial products.

1

98x 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.

Check your answer with estimation!

98 100x 12 x 12 1196 ~1200 +980 1176

(Estimated answer is very close the exact answer and let's us know if our answer is reasonable.)

REVIEW the STEPS

Step 1:

How do you multiply by 2-digit numbers?

Multiply by the ONES place. Regroup if necessary.

REVIEW the STEPS

Step 2:

How do you multiply by 2-digit numbers?

Multiply by the TENS PLACE. Regroup.

REVIEW the STEPS

Step 3:

How do you multiply by 2-digit numbers?

Add the PARTIAL PRODUCTS.

Easy as ....

Find each product following the steps:1. 44 2. 26 3. 17 4. 35 5. 45x 23 x 18 x 23 x 71 x16

Easy as ....

Independent Practice

Estimate first to see what the answer will be closest to!1. 44 2. 26 3. 17 4. 35 5. 45x 23 x 18 x 23 x 71 x16

40 30 20 40 50x 20 x 20 x 20 x 70 x 20 800 600 400 2800 1000

Independent Practice

How did you do?1. 44 2. 26 3. 17 4. 35 5. 45x 23 x 18 x 23 x 71 x16

1132 208 51 35 1270+ 880 + 260 +340 + 2450 + 450 1,012 468 391 2,485 720

Independent Practice

Quick Check

Math

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

Quick Check

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

In your Math Notebook Response Example

Quick Check

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

In your Math Notebook Response Example

Quick Check

Writing to explain: How can finding the product of 5 x 700 help you check the product of 5 x 789? 47489 5 x 9 = 45 x 5 5 x 80 = 400 3,945 5x 700 = 3500

3945

In your Math Notebook Response Example

Quick Check

Writing to explain: The estimate answer of 4,000 was a very close estimate! 47489 5 x 9 = 45 x 5 5 x 80 = 400 3,945 5x 700 = 3500

3945

In your Math Notebook Response Example

Today you learned how to multiply 2 -digit by 2 digit Numbers!

Good Work with this

lesson.