Mixed Numbers to Fractions uses number line models to demonstrate how a number in mixed form can be renamed in fraction form.

The illustration below was made by Mixed to Fraction Designer. It shows the mixed number 2 3/5. You are to write 2 3/5 in fraction form, with only a numerator and denominator.

In this example, you will notice that
the arrow is pointing to the 13th mark after 0, giving a numerator
of 13. The number of parts between each whole unit is 5, giving
a denominator of 5 for a fraction of 13/5. Some textbooks call a
fraction such as this * improper*, where the numerator is equal to or larger
than the denominator. There is nothing improper with the fraction 13/5. This is better known as the fraction form or a/b form of the number.

To write the example, you can think of each whole unit as 5/5. So in the above example you would have:

Another way to arrive at the numerator 13 is to multiply the whole number 2 by the denominator 5 and then add the numerator 3 as in this example: