To convert the whole number 5 into a fraction, you can represent it as 5/1. This means that the number 5 is equivalent to 5 whole parts out of 1 whole.
The denominator in this case is 1. The reason we use 1 as the denominator is that any whole number can be expressed as that number over one. So, 5 as a fraction is simply 5 divided by 1.
In addition, you can also express it in other forms, like 10/2 or 15/3, where the numerator can change but the value remains 5. However, the simplest and most straightforward way to write it is 5/1 with 1 as the denominator.