The Marble Problem
Probability
Level
3
You have a bag with 300 marbles and every marble has two colors. If 70% of the marbles are red and 50% of those are yellow and 60% are green. How many are blue?
60
105
90
It is impossible
35
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1 solution
To solve this you have to imagine you have 100 marbles. Then you take it one step at a time. First you say that 70 marbles are half colored and then that 35 are done. Now you have 30 marbles without a color and 35 half done. The only thing you can do now is make the 30 marbles halfway and leave 5 also halfway. Otherwise, you would have 5 marbles with no color at all with only one color left. Now you know that 35 marbles need one color, that is 35%, and 35% of 300 is 105.