Is this for your homework? If so, you shouldn't ask for help. The reason for homework is kind of basically a self study. Next time on a test, you won't know how. What you do is, you need to first figure out how many marbles in total. 5 blue, 8 green and 3 yellow. How much in total? = 16. So that will be the denominater. (number on the bottom). Then it asks you what are the chances of NOT GETTING A BLUE. That is the key. Subtract how many blue (in this case, 5) from the total (16) which is 11.This will be your numerator. (number on the top). And so, you'd get the answer. 11 over 16 or 11/16. If you're only looking for the answer, your being lazy (no offence) because your relying on others too much just for something as easy as this. Its not 5/16 because its asking for the probability of getting any of the 3 colors BUT Blue. So you would need to take blue out of the way to have only green and yellow in the box. A revised version of the question would be; A box contains five blue, eight green and three yellow marbles. If a marble is selected at random, what are the chances of getting anything BUT blue?