The ratio of balls in a bag is as follows: 5 green: 1 yellow: 6 black
how many balls would there be in the bag if you have 72 black balls?

The ratios are  5 Green / total, 1 yellow / total, 6 black / total
all together 5 + 1 + 6 = 12
6/12 = 1/2
so for every black ball, there is 1 other ball
if you have 72 black balls there are
2 x 72 balls = 144 balls