1. Module 3 Lesson 20 Use place value strategies and the associative property n × (m × 10) = (n × m) × 10 (where n and m are less than 10) to multiply multiples of 10.

2. Fluency Practice 2 × 3 = ____. Say the multiplication equation in unit form 2 ones × 3 ones = 6 ones Say it in standard form. 2 × 3 = 6

3. Fluency Practice 2 tens × 3 = ____. Say the multiplication equation in unit form 2 tens × 3 ones = 6 tens Say it in standard form. 20 × 3 = 60

4. Fluency Practice 4 × 2 = ____. Say the multiplication equation in unit form 4 ones × 2 ones = 8 ones Say it in standard form. 4 × 2 = 8

5. Fluency Practice 4 tens × 2 = ____. Say the multiplication equation in unit form 4 tens × 2 ones = 8 tens Say it in standard form. 40 × 2 = 80

6. Fluency Practice 5 × 3 = ____. Say the multiplication equation in unit form 5 ones × 3 ones = 15 ones or 1 ten and 5 ones Say it in standard form. 5 × 3 = 15

7. Fluency Practice 5 × 3 tens = ____. Say the multiplication equation in unit form 5 ones × 3 tens= 15 tens or 1 hundred, 5 tens and 0 ones. Say it in standard form. 5 × 30 = 150

8. 7 x 6 = _____ Say the multiplication equation 42 70 x 6 = _____Say the multiplication equation 420

9. 4 x 9 = _____ Say the multiplication equation 36 40 x 9 = _____Say the multiplication equation 360

10. 8 x 8 = _____ Say the multiplication equation 64 80 x 8 = _____Say the multiplication equation 640

11. Write in the Parentheses 4 × 5 = 2 × 2 × 5. What is 4 x 5? On your personal white board, copy the equation. Then, underneath the equation, write another equation with parentheses in the correct place … the parentheses should match the problem on the left side of the equation. Then, Solve! 4 × 5 = (2 × 2) × 5. 20 = 4 x 5 20 = 20

12. Write in the Parentheses 6 × 4 = 6 x 2 x 2. What is 6 x 4? 6 × 4 = 6 x (2 x 2). 24 = 6 x 4 24 = 24 On your personal white board, copy the equation. Then, underneath the equation, write another equation with parentheses in the correct place … the parentheses should match the problem on the left side of the equation. Then, Solve!

13. PROBLEM OF THE DAY Model 3 × 4 on a place value chart. Then, explain how the array can help you solve 30 × 4 tensones Think about the problem in UNIT form. 3 ones x 4 ones = 12 ones If we multiply by 3 tens x 4 ones – the number will be the same – the only thing changing is our unit. INSTEAD OF 12 ONES WE HAVE 12 TENS!

14. CONCEPT DEVELOPMENT (40 × 2) Ten times what number gives us a product of 40? Let’s rewrite our equation (10 × 4) × 2. Why do you think I put 10 × 4 in parentheses? The parentheses remind us that we put 10 × 4 where 40 used to be.

15. (10 × 4) × 2 Rewrite the equation on your dry erase board. Use the Parentheses to group the numbers differently. 10 × (4 × 2) Is this problem friendlier than 40 x 2? 10 × (4 × 2) 10 x 8

16. CONCEPT DEVELOPMENT (20 x 3) Ten times what number gives us a product of 20? Let’s rewrite our equation (10 × 2) × 3. Why do you think I put 10 × 2 in parentheses? The parentheses remind us that we put 10 × 2 where 20 used to be.

17. (10 × 2) × 3 Rewrite the equation on your dry erase board. Use the Parentheses to group the numbers differently. 10 × (2 x 3) Is this problem friendlier than 20 x 3? 10 × (2 × 3) 10 x 6

18. CONCEPT DEVELOPMENT (30 x 3) Ten times what number gives us a product of 30? Let’s rewrite our equation (10 × 3) × 3. Why do you think I put 10 × 3 in parentheses? The parentheses remind us that we put 10 × 3 where 30 used to be.

19. (10 × 3) × 3 Rewrite the equation on your dry erase board. Use the Parentheses to group the numbers differently. 10 × (3 x 3) Is this problem friendlier than 30 x 3? 10 × (3 × 3) 10 x 9

20. Concept Development Part II Use the chart to write a multiplication equation in unit form. 3 × 6 ones = 18 ones

21. Now, I want to multiply 18 ones by ten. Watch as I show this on the chart. I redraw dots into the tens place and draw an arrow to remind myself that they shift to the next unit. Let’s multiply our 3 groups of 6 ones by 10.

22. 6 ones × 10 = 6 tens Now, I want to multiply 6 tens by 3. How many rows do I need to add to show 3 rows of 6 tens? 2 more rows 3 × (6 × 10) How does my array show this expression? What is the answer to 3 × 6 tens in unit form? 18 tens Or 180!

23. Compare the equations (3 × 6 ones) × 10 and 3 × (6 × 10) What do you notice about the factors we used? The factors are the same! 3, 6, and 10. The units are different, and so is the order. What we multiply first is different.

24. PROBLEM SET