Multiply a decimal by 10, 100, 1000,..

### 1.1. Knowledge to remember

**a) **Example 1: 27,867 x 10 = ?

27.867 x 10 = 278.67

__Comment:__ If we move the comma of the number 27,867 one digit to the right, we also get 278.67.

**b) **Example 2: 53.286 x 100 = ?

53.286 x 100 = 5328,600

**Comment:** If we move the comma of the number 53.286 to the right by two digits, we also get 5328.6.

To multiply a decimal number by 10,100,1000.., we just need to move the comma of that number to the right one, two, three… digits respectively.

### 1.2. Solve textbook exercises page 57

**Lesson 1 Textbook page 57**

Multiplication:

a) 1.4×10 b) 9.63×10

2.1×100 25.08×100

7.2×1000 5.32×1000

c) 5,328×10

4.061×100

0.894×1000

__Solution guide:__

a) 1.4×10=14

2.1×100=21

7.2×1000=7200

b) 9.63×10=96.3

25.08×100=25

5.32×1000=5320

c) 5.328×10=53.28

4.061×100=406.1

0.894×1000=894

Lesson 2 Textbook page 57

Write the following measurements as centimeters:

10.4dm; 12.6m; 0.856m; 5.75dm.

__Solution guide:__

+ 1dm = 10cm so 10.4dm = 10cm x 10.4 = 104cm.

+ 1m = 100cm so 12.6m = 100cm x 12.6 = 1260cm;

+ 1m = 100cm so 0.856m = 100cm x 0.856 = 85.6cm;

+ 1dm = 10cm so 5.75dm = 10cm x 5.75 = 57.5cm

Lesson 3 Textbook page 57

A plastic can contains 10 liters of kerosene. Know the weight of a liter of kerosene

$0,8kg$, empty can weigh cân

$\mathrm{first},3kg$. How many kilograms does that can of kerosene weigh?

__Solution guide:__

$\mathrm{ten}\phantom{\rule{0ex}{0ex}}l$

kerosene weighing kilograms is:

0.8×10=8(kg)

That whole can of kerosene weighs kilograms:

8+1.3=9.3(kg)

Answer: 9.3kg.

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