48/80 In simplist form ?
You can get this by finding a common factor. You can do that several times if you need to to make it easier. For example, we can divide num/denominator by 2, and you get: 24/40 Then we can divide by 2 again, and you get: 12/20 Then we can divide by two again, and you get: 6 / 10 Then one more time, you get: 3 / 5 The other option is to notice common factors that are greater than 2 or 3. So we could just have divided by 16 in this case and gone straight from 48/80 to 3/5.
The important thing is that you stop at 3 / 5 because there is no longer a number that divides evenly into both the top and the bottom (in this case, there is no number that divides evenly into either of them, as they are prime).