So you have 60 all together and the problem tells you that there are 36 white ones, so you will subtract 36 from 60, giving 24. If there is an equal amount of red and blue marbles, you would divide 24 by 2, giving you 12. You will then take those 12 blue marbles and divide by the 60 all together to get your percentage. 12 is 1/5 of 60 and 1/5 is equivalent to 20%.
