Fractions
In the real world, there are not only whole numbers. E.g. bread can be cut into two halves and pizza into eight slices. To describe them we use fractions. They simply tell us how many parts of a whole we have.
Fractions show parts of whole numbers. Each fraction consists of a numerator and a denominator. The numerator is the top digit that represents how many equal parts the fraction contains. The denominator is the bottom digit that represents how many equal parts the whole is broken into:
To find the fraction that is missing to make 1 whole, look at how many equal parts the whole is divided into. A whole means that all parts are filled. So if the whole is divided into 4 parts, then the whole is 4/4. If 3/4 is shaded, then 1/4 is missing. The denominator stays the same, and we only find how many parts are still needed.
There are many ways to write the same fraction. In the picture, you can see that $1/2$, $2/4$, $3/6$, and $4/8$ all represent the same amount. Even though the numerators and denominators are different, the shaded parts of the boxes always show the same half of the whole. To make one whole, we need the other half, which is also $1/2$.
