Find a factor of multiplication

### 1.1. Knowledge to remember

– The relationship between products and factors in multiplication.

– How to find an unknown factor in a product.

### 1.2. Math forms

**Type 1: Perform multiplication and division calculations.**

I recall the knowledge of the multiplication table from 1 to 5 and the division table of 2, 3

**Form 2: Find the unknown factor.**

To find a factor we divide the product by the other factor.

**Form 3: Math quizzes.**

– Read and analyze the problem: The problem gives information about the value of many groups, the value of each group, asking to find the number of equal groups.

– Find the solution of the problem: To find the number of groups, divide the value of many groups by the value of each group.

– Present the solution.

– Check the solution and answer of the problem.

### 1.3. Solving Textbook Exercises page 116

**Lesson 1**

Mental arithmetic:

2 x 4 = 3 x 4 = 3 x 1 =

8 : 2 = 12 : 3 = 3 : 3 =

8 : 4 = 12 : 4 = 3 : 1 =

__Solution method__

Mentally calculate the value of multiplication and division within the range learned and then fill in the results in the blanks.

__Solution guide__

2 x 4 = 8 3 x 4 = 12 3 x 1 = 3

8 : 2 = 4 12 : 3 = 4 3 : 3 = 1

8 : 4 = 2 12 : 4 = 3 3 : 1 = 3

**Lesson 2**

Find x (by pattern):

a) x × 2 = 10

x = 10 : 2

x = 5

b) x × 3 = 12

c) 3 × x = 21

__Solution method__

To find a factor, we divide the product by the other factor.

__Solution guide__

b) x × 3 = 12

x = 12 : 3

x = 4

c) 3 × x = 21

x = 21 : 3

x = 7

**lesson 3**

Find y:

a) yx 2 = 8

b) yx 3 = 15

c) 2 xy = 20

__Solution method__

To find a factor, we divide the product by the other factor.

__Solution guide__

a) yx 2 = 8

y = 8: 2

y = 4

b) yx 3 = 15

y = 15 : 3

y = 5

c) 2 xy = 20

y = 20 : 2

y = 10

**Lesson 4**

There are 20 students studying, each table has 2 students. How many desks are there in all?

__Solution method__

To find the number of tables, we divide the number of students by 2.

__Solution guide__

The number of desks is:

20 : 2 = 10 (table)

Answer: 10 desks.

### 1.4. Solving Textbook Exercises page 117

**Lesson 1**

Find x:

a) x × 2 = 4

b) 2 × x = 12

c) 3 × x = 27

__Solution method__

To find a factor, divide the product by the other factor.

__Solution guide__

a) x × 2 = 4

x = 4: 2

x = 2

b) 2 × x = 12

x = 12 : 2

x = 6

c) 3 × x = 27

x = 27 : 3

x = 9

**Lesson 2**

Find y:

a) y + 2 = 10

b) yx 2 = 10

c) 2 xy = 10

__Solution method__

– Find the term equal to the sum minus the other term.

Find a factor equal to the product divided by the other factor.

__Solution guide__

a) y + 2 = 10

y = 10 – 2

y = 8

b) yx 2 = 10

y = 10 : 2

y = 5

c) 2 xy = 10

y = 10 : 2

y = 5

**lesson 3**

Write the correct number in the blank:

__Solution method__

Find the missing product and factor in each multiplication and fill in the appropriate number in the blank.

__Solution guide__

**Lesson 4**

There are 12kg of rice divided equally among 3 bags. How many kilograms of rice are in each bag?

__Solution method__

To find the answer we divide 12kg by the number of bags.

__Solution guide__

The number of kilograms of rice in each bag is:

12 : 3 = 4 (kg)

Answer: 4 kg

**Lesson 5**

There are 15 flowers in the vases, each vase has 3 flowers. How many flower vases can I arrange?

__Solution method__

To find the solution, we divide the number of flowers by 3.

__Solution guide__

The number of flowerpots is:

15 : 3 = 5 (flowerpot)

Answer: 5 flowerpots

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