Natural numbers

In this article, you will learn everything you need to know about natural numbers and you will put it into practice in various exercises.
Shall we start?

A natural number must be whole and positive.
Observe: For a number to be considered natural, it must meet both conditions, be positive and whole.
In everyday life, we use natural numbers all the time, almost every time we have to count or calculate something.
What about $0$?
$0$ is also a natural number.
Natural numbers are infinite: All the positive whole numbers from $0$ to infinity are called natural numbers.
With them, we can count anything we want and also add, subtract, multiply, and divide.

$21, 0, -4, 7$

Solution:
According to its definition, a natural number is a whole and positive number. Therefore:
$21$ : Natural number –> whole and positive.
$0$ : Natural number –> is included within the set of natural numbers.
$-4$ : Number that is not natural –> it is negative (does not meet the condition of being positive)
$7$ : Natural number–> whole and positive.

$1, -15, -\frac{2}{3}, \frac{7}{6}$

Solution:
According to its definition, a natural number is a whole and positive number.

Therefore:
$1$  Natural number – whole and positive.
$-15$  Number that is not natural - it is negative (does not meet the condition of being positive)
$-\frac{2}{3}$  Number that is not natural - negative and also not whole
$\frac{7}{6}$  Number that is not natural - Not whole

$2\frac{4}{5} , 13 , -100 , 4.5$

Solution:
$4.5$  Number that is not natural - Although it is positive, it is not an integer.
$-100$ Number that is not natural - It is negative (does not meet the condition of being positive)
$13$  Natural number – Positive and also an integer
$2\frac{4}{5}$   Number that is not natural - Although it is positive, it is not an integer.

$(2+3) \times ⬜ +15=40$

Solution:
In this exercise, there are only natural numbers, we need to find out which one would fit in the place of the square.
First, let's find out what the result of the parentheses is and rewrite the exercise.

We will obtain:
$5 \times ⬜ +15=40$
Now we can say that $5$ times something $+ 15$ equals $40$.
If we subtract $15$ from both sides we will get:
$5 \times ⬜ =25$
Now let's think, what number multiplied by five will give us $25$.
We could also simply divide both sides by $5$ and obtain: 
$⬜ = 5$

The general price of a pair of pants and four shirts is $600$$.
The price of a pair of pants is equivalent to the price of $2$ shirts.

1. What is the price of a pair of pants?
2. What is the price of a shirt?

Solution:
First, let's organize the data.
We know that the price of a pair of pants is equal to the price of 2 shirts.
If we name the price of a shirt $X$ we can say that the price of a pair of pants is $2X$.
We also know that a pair of pants and $4$ shirts cost $600$$ .
Let's write it as an exercise and we will get:
$2X+4X=600$
Let's solve the equation and it will give us:
$6X=600$
$X=100$

Observe –> $X$ represents the price of $1$ shirt.
$​​2X$ is the price of a pair of pants $1$.
If $X=100$ then the answer will be:
The price of a pair of pants is $200$$.
$100 \times 2=200$
The price of a shirt is $100$$.