Ian has 20 balls of four colors: yellow, green, blue, and black. 17 of them are not green, 5 are black, and 12 are not yellow. how many blue balls does ian have

So firstly, we have to find out how many are green and yellow. For green subtract 17 from 20 and for yellow subtract 12 from 20:

Next, add up the total amount of balls that are green, yellow, and black:

Lastly, subtract 16 from 20:

one that is bigger than 3 1/2