What to do: Take the two numbers 3 and 15 and put the number of green (3) as the numerator and the number of total colors (15) as the denominator as shown here 3/15 and then you simplify it. How many time does 3 go in to 3, 1 time and how many times does 3 go in to 15, 5 times so it would be 1/5.