This is a Clilstore unit. You can .

Now that we know what a natural number is, let's go with the operations.

First we are going to study addition. Please, click on the play button on your left.

Now, you are supposed to be able to do a multi-digit addition of natural numbers.

Do you know what is the name of the terms of an addition?

OK, they are called **addends** (a and b), and the result is the **sum **(c). **a + b = c**

Knowing that terms, you are ready to know about the properties of the addition, which are:

**1. Commutative**: The order of the addends does not change the addition.

**a + b = b + a **

2 + 5 = 5 + 2

7 = 7

**2. Associative**: It doesn't matter the way in which the addends are grouped, because the result does not change.

**(a + b) + c = a + (b + c) **

(2+3) + 5 = 2 + (3+5)

5 + 5 = 2 + 8

10 = 10

**3. Closure**: The sum of** two natural numbers** is also a ** natural number**.

**a + b **

**4. Additive identity**: The 0 is the identity element of the addition because every number added with it gives the same number.

**a + 0 = a **

3 + 0 = 3

You can click on SUPPORT 1 button, where you will find a pdf file with an addition table of the numbers from 1 to 9.

Now it's the time for the subtraction. First of all, please watch the VIDEO 2, by clicking on its button.

In this case, the terms of a** subtraction** are called:** the minuend, a,** and** the subtrahend, b**, and the result, **c**, is called** the difference**. **a - b = c**

And the properties of the subtraction are:

1. **No closure**: The result of** subtracting two natural numbers** is not always another** natural number**.

2 − 5

**2. No commutative: **The order in which you make the subtraction change it.

a - b ≠ b - a

5 − 2 ≠ 2 − 5

And now we are ready to do also a multi-digit subtraction of natural numbers.

Do you want to check it? Let's do TASK 1, with some multi-digit additions and subtractions.

Short url: http://multidict.net/cs/4150