Divide a decimal by 10,100,1000..

### 1.1. Knowledge to remember

**a)** __Example 1__: 213.8: 10 = ?

213.8: 10 = 21.38

** Comment**: If we move the comma of the number 213.8 to the left one digit, we also get 21.38.

**b)** __Example 2__: 89.13 : 100= ?

89.13 : 100= 0.8913

** Comment:** If we move the comma of the number 89.13 to the left by two digits, we also get 0.8913

Want to divide a decimal number by 10, 100, 1000, … we just need to move the comma of that number one, two, three, … digit respectively to the left.

### 1.2. Solution of textbook exercises page 66

**Lesson 1 Textbook page 66**

Mental arithmetic:

a) 43.2:10 0.65:10

432.9:10

$0$13.96:1000

b) 23.7:10 2.07:10

2.23:100 999.8:1000

*Solution guide:*

a) 43.2:10=4.32 0.65:10=0.065

432.9:100=4.329 13.96:1000=0.01396

b) 23.7:10=2.37 2.07:10=0.207

2.23:100=0.0223 999.8:1000=0.9998

Lesson 2 Textbook page 66

Calculate and compare the results:

a) 12.9:10 and 12.9×0.1

b) 123.4:10

$0$and 123.4×0.01

c) 5.7:10 and 5.7×0.1

d) 87.6:100 and 87.6×0.01

*Solution guide:*

a) 12.9:10=1.29 12.9×0.1=1.29

Hence: 12.9:10=12.9×0.1

b) 123.4:100=1,234 123.4×0.01=1,234

Hence: 123.4:100=123.4×0.01

c) 5.7:10=0.57 5.7×0.1=0.57

Hence: 5.7:10=5.7×0.1

d) 87.6:100=0.876; 87.6×0.01

$=0,876$Hence: 87.6:100=87.6×0.0

$\mathrm{first}$Lesson 3 Textbook page 66

A stock of rice has

$537,25$tons of rice. One-tenth of the rice in stock was taken out. How many tons of rice are left in the warehouse?

*Solution guide:*

The amount of rice taken out is:

537.25:10=53,725 (ton)

The remaining rice in stock is:

537.25−53,725=483,525(ton)

Answer: 483,525 tons

.

=====

## Leave a Reply