Understand How to Use Arrays to Multiply with 6,7 & 8

Key Concepts

• Use arrays to multiply with 6.
• Use arrays to multiply with 7.
• Use arrays to multiply with 8.

3.3 Apply properties: 6 ,7 and 8 as factors

Some basic multiplication facts are needed to follow for multiplying numbers. In array model, we are using the following facts.

Use 5s facts and 1s facts to help multiply by 6.

Use 5s facts and 2s facts to help multiply by 7.

Use double 4s facts to help multiply by 8.

3.3.1 Use arrays to multiply with 6

Example1:

Ming plans to harvest leafy vegetables in his garden. He planted 6 rows of plants. Each row has 7 plants. How many plants has he planted?

Solution:

Step1: Use 5 as a fact and 1 as a fact.

Step2: Draw an array for each multiplication sentence.

6 x 7 is 6 rows of 7.

5 sevens plus 1 more seven.

Step3: Multiply 5 x 7 = 35

Step4: Multiply 1 x 7 = 7

Step5: Add 35 + 7 = 42

So, 6 x 7 =42                                                                                                                                    

3.3.2 Use arrays to multiply with 7

Example1:

Ming arranged 7 rows of toy cars in his cupboard. Each row has 6 cars. Find the total number of cars Ming arranged?

Solution:

Step1: Use 5 as a fact and 2 as a fact.

Step2: Draw an array for each multiplication sentence.

7 x 6 equals 7 rows of 6.

5 sixes plus 2 sixes.

Step3: Multiply 5 x 6 = 30

Step4: Multiply 2 x 6 = 12

Step5: Add30+12 = 42

So, 7 x 6 = 42

3.3.3 Use arrays to multiply with 8

Example1:

Chrissy bought some crayons for art class. She arranged 8 rows of crayons. Each row has 4 crayons. How many crayons did Chrissy arrange?

Solution:

One way:

Use 2 as a factor to find 8 x 4.

8 x 4 equals 4 groups of 2 fours.

Add 8 + 8 + 8 + 8 = 32

So, 8 x 4 =32

Another way:

Double 4 as a factor to find 8 x 4.

8 x 4 equals 4 fours plus 4 fours.

Add 16 + 16 = 32

So, 8 x 4 = 32

Exercise:

1. Multiply the following.  Draw pictures or use counters to help.
a. 6 x 9 = ________
b. 6 x 3 = ________
c. 7 x 4= ________
d. 7 x 9= ________

2. Find 4 times 5.

3. Find the product. You may draw pictures to help.

4. Multiply. Draw pictures or use counters to help.
a. 8 x 6 = ___________
b. 5 x 8 = ___________
c. 8 x 7 = ___________

5. Match each ice cream scoop to its proper cone.

6. Multiply 8 times 5. Write and solve a multiplication equation.

7. Multiply 7 times 6. Write and solve a multiplication equation.

8. The students who will receive prizes for games, are standing in 6 equal rows. There are 8 students in each row. Find the total number of students who will receive prizes.

9. There are 7 rows of 5 chairs in the class. How many chairs are there in the class?

10. Aaron bought 6 packs of greeting cards. There are 5 cards in each pack. How many greeting cards did Aaron buy in all?

Concept map:

What have we learned:

• Understand about facts.
• Understand how to use arrays to multiply with the 6.
• Understand how to use arrays to multiply with the 7.
• Understand how to use arrays to multiply with the 8.
• Understand how to separate array into equal groups.
• Understand how can use doubles to multiply with 8.