20+23+20+15= 78
78 is the total amount of marbles in the jar. It is our denominator.
20/78 = green, simplify = 10/39 is the probability you will pick green.
23/78 = orange, 23/78 is simplified so it is the probability you will pick orange.
20/78 = red, simplify = 10/39 is the probability you will pick red
