First, you find the biggest number that you can divide 24, 30, and 12 by. I would go with 6, because it will simplify all the numbers into the simplest forms possible in this equation. Then, divide each number by 6.
24/6= 4
30/6= 5
12/6= 2
The answer:
4 : 5 : 2
Hope I could be of help:)
