Multiply by 10,100,1000…., Divide by 10,100,1000….

### 1.1. Knowledge to remember

**first. **a) 35 x 10 = ?

35 x 10 = 10 x 35

= 1 dozen x 35 = 35 tens = 350

So: 35 x 10 = 350.

When multiplying a natural number by 10, we just need to add a 0 to the right of that number.

b) Otherwise, from 35 x 10 = 350

we have: 350 : 10 = 35.

When dividing a round number by 10, we just need to remove a zero to the right of the number.

**2. **Similarly, we have:

a) 35 x 100 = 3500 b) 35 x 1000 = 35000

3500 : 100 = 35 35000 : 1000 = 35

**3.** General comment :

*When multiplying a natural number by 10, 100, 1000 … we simply add one, two, three … zeros to the right of the number.**When dividing a number round ten, round hundred, round thousand, … by 10, 100, 1000, … we just need to remove one, two, three … zeros to the right of that number.*

### 1.2. Solving Textbook Exercises

**Lesson 1: **Mental arithmetic

a) 18 × 10 82 × 100 256 × 1000

18 × 100 75 × 1000 302 × 10

18 × 1000 19 × 10 400 × 100

b) 9000 : 10 6800 : 100 20020 : 10

9000 : 100 420 : 10 200200 : 100

9000 : 1000 2000 : 1000 2002000 : 1000

**Solution guide:**

- When multiplying a natural number by 10, 100, 1000, … we just need to add one, two, three, … digit 0 to the right of that number.
- When dividing a number round ten, round hundred, round thousand, …. by 10, 100, 1000, … we just need to remove one, two, three, … zeros to the right of that number.

a) 18 × 10 = 180 82 × 100 = 8200 256 × 1000 = 256000

18 × 100 = 1800 75 × 1000 = 75000 302 × 10 = 3020

18 × 1000 = 18000 19 × 10 = 190 400 × 100= 40000

b) 9000 : 10 = 900 6800 : 100 = 68 20020 : 10 = 2002

9000 : 100 = 90 420 : 10 = 42 200200 : 100 = 2002

9000 : 1000 = 9 2000 : 1000 = 2 2002000 : 1000 = 2002

**Lesson 2:** Write the correct number in the dot

300kg = … 70kg weight = … oats

*Making : * 800kg = … weights

We have: 100kg = 1 ton 300 quintals = … tons

Mental: 300 : 100 = 3 120 quintals = … tons

So: 300kg = 3 quintals 5000kg = … tons

4000g = … kg

- We make the remaining sentences similar to the example.

70kg = 7 oats 120 quintals = 12 tons

800kg = 8 weights 5000kg = 5 tons

300 quintals = 30 tons 4000g = 4kg

.

=====

## Leave a Reply