To have a number in simplest form is to have the number at a point where it can not be divided into anymore whole numbers. For example, 4/8 can be simplified into 1/2, but 3/5 can not be simplified. There is nothing they can both be divided by to become whole numbers. So, let's walk through 2-3. 2 - 3 = -1. therefore, we can change the problem into 2/1 - 3/1. We don't have to, but it might help. Then we know that 2/1 - 3/1 = -1/1. Then we look at -1/1. Can it be divided by anything to become a new whole number? No. Therefore, we can safely take away the denominator, and call it -1. So -1 is in simplest form. :D I hope that helped.