Math 5 Multiplication: 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. $5.91 $17.03 $11.85 $0.97

Round to the nearest dollar. Math Warm-up Round to the nearest dollar. $5.91 $6.00 $17.03 $17.00 $11.85 $12.00 $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?

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.

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?

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.

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 = 27 + 2 zeros = 2700.

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.

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

STEP 2: Multiply by the TENS place. (partial product with tens only) 1 98 x 12 196 980 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 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.

Check your answer with estimation! 98 100 x 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.)

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

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

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

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

Estimate first to see what the answer will be closest to! Independent Practice Estimate first to see what the answer will be closest to! 1. 44 2. 26 3. 17 4. 35 5. 45 x 23 x 18 x 23 x 71 x16 40 30 20 40 50 x 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. 45 1. 44 2. 26 3. 17 4. 35 5. 45 x 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

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

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.

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.

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? 47489 5 x 9 = 45 x 5 5 x 80 = 400 3,945 5x 700 = 3500 3945

Quick Check In your Math Notebook Response Example 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

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