Number 1 in multiplication and division

### 1.1. Knowledge to remember

Special property of 1 in multiplication and division.

### 1.2. Math forms

**Form 1: Calculate**

Perform calculations when multiplying a number by 1 or dividing any number by 1.

**Form 2: Find the missing element**

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

– To find the divided number, we take the merchant with the divisor.

**Form 3: Compare**

– Perform calculations.

– Compare the calculated value.

### 1.3. Solving Textbook Exercises

**Lesson 1**

Mental arithmetic:

1 x 2 = 1 x 3 = 1 x 5 =

2 x 1 = 3 x 1 = 5 x 1 =

1 x 1 = 2 : 1 = 3 : 1 =

5 : 1 = 1 : 1 =

__Solution method__

Any number multiplied by 1 equals the same number.

Any number divided by 1 is equal to that number.

__Solution guide__

1 x 2 = 2 1 x 3 = 3 1 x 5 = 5

2 x 1 = 2 3 x 1 = 3 5 x 1 = 5

1 x 1 = 1 2 : 1 = 2 3 : 1 = 3

5 : 1 = 5 1 : 1 = 1

**Lesson 2**

Number ?

… x 2 = 2 5 x …= 5 …. : 1 = 3

… x 1 = 2 5 : …= 5 …. x 1 = 4

__Solution method__

Any number multiplied by 1 equals the same number.

Any number divided by 1 is equal to that number.

Using the above knowledge, we find the missing number of calculations.

__Solution guide__

1 x 2 = 2 5 x 1 = 5 3 : 1 = 3

2 x 1 = 2 5 : 1 = 5 4 x 1 = 4

**lesson 3**

Calculate:

a) 4 x 2 x 1 =

b) 4: 2 x 1 =

c) 4 x 6 : 1 =

__Solution method__

Perform calculations from left to right.

__Solution guide__

a) 4 x 2 x 1 = 8 x 1 = 8

b) 4: 2 x 1 = 2 x 1 = 2

c) 4 x 6 : 1 = 24 : 1 = 24

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