Look at the fact that there are 45 marbles first. There is no clue just how many blues there might be. but there should not be as many as 18. The only way you can solve this is with a proportion. You can also ask yourself if Jon draws 45 instead of 60 times, how many marbles will he draw.
18/60 = x / 45 Cross multiply
18*45 = 60*x
810 = 60x
810 / 60 = x
x = 13.5
He can't draw 1/2 a marble. The answer is either 13 or 14 depending on what you have been told about rounding. Statistically I would pick 13 because it is a conservative choice.
