What is a 18 out of 21?

In the context of fractions, 18 out of 21 can be simplified by dividing both the numerator (18) and the denominator (21) by their greatest common factor, which is 3. This simplifies to 6/7, which is the equivalent fraction. This means that if you have 18 out of 21 items, it is the same as having 6 out of 7 items.