Multiplication Using Arrays

Key Concepts

• Use arrays to multiply with 3.
• Use arrays to multiply with 4.

3.2 Apply properties: 3 and 4 as factors 

What is meant by factors? 

 A factor is a number that divides the given number without any remainder. 

• The number 1 is the smallest factor of every number. 
• Every number will have a minimum of two factors, 1 and the number itself. 
• A number that has only two factors, 1 and the number itself, is called a prime number. 

What are the factors of 3? 

Factors of 3 are, 1 and 3 

What are the factors of 4? 

Factors of 4 are 1, 2, and 4 

4 equals 2 x 2 

4 = 2² 

Real-life applications of factors: 

Dividing something into equal pieces, exchanging money, comparing prices, understanding time and making calculations. 

3.2.1 Use arrays to multiply with 3 

Example1: 

Ria went to a playground. She arranged 3 rows of balls in the playground. There are 5 balls in each row. How many balls did Ria arrange? 

Find 3 x 5 

Solution: 

Step1:  Make an array for each multiplication sentence. 

3 x 5 is 3 rows of 5. That is 2 fives plus one more five. 

Step2 : Multiply 2 x 5=10 

Step3 : 1 x 5  =  5.  

Step4 :  10+5  =  15. 

Step5 : Multiply 3 x 5 =15  

Ria arranged 15 balls. 

Example2: 

Steven arranged 3 rows of strawberries in a plate. He put 4 strawberries in each row. How many strawberries did Steven arrange in the plate? 

Find 3 x 4. 

Solution: 

Step1:  Make an array for each multiplication sentence.  

3 x 4 is 3 rows of 4. That is 2 fours plus one more four. 

Step2: Multiply 2 x 4=8. 

Step3 : 1 x 4  =  4.  

Step4 :  8+4 =  12. 

Step5 : Multiply 3 x 4 =12.  

Steven arranged 12 strawberries. 

3. 2. 2 Use arrays to multiply with 4 

Example1: 

Michael invited some of his friends to his house. He arranged 4 rows of cupcakes on the table for his friends. He put 5 cupcakes in each row. How many cupcakes did he arrange on the table? 

Find 4 x 5 

Solution: 

Step1: Make an array for each multiplication sentence. 

4 x 5 is 4 rows of 5 

That is 2 fives plus 2 fives 

Step2: Multiply 2 x 5 = 10 

Step3: Add 10 + 10 = 20 

So, 4 x 5 = 20 

The boy arranged 20 cupcakes. 

Example2: 

John arranged 4 rows of chairs for a meeting. He put 4 chairs in each row. How many chairs did John arrange? 

Solution: 

Step1: Make an array for each multiplication sentence. 

4 x 4 is 4 rows of 4. 

That is 2 fours plus 2 fours. 

Step2: Multiply 2 x 4 = 8 

Step3: Add 8 + 8 = 16 

So, 4 x 4 = 16 

John arranged 16 chairs for the meeting. 

Exercise:

1. Find 4 x 6

2. Multiply the following:

3. Match the following:

4. Chrissy arranged 3 rows of plants in her garden. She put 8 plants in each row. How many plants did Chrissy arrange?

5. Fill in the blanks:

a. 3 x 5=_

b. 4x_= 16

c. 3×8=_

d. 4x = 28

6. David arranged 3 rows of bananas. He put 4 bananas in each row. How many bananas did David arrange?

7. Ria saw a goat farm which has 3 pens. Each pen has 5 goats. Find the number of goats on the farm.

8. Steven walks 4 miles each day. How many miles does Steven walk in one week?

Concept map: