SOLUTION: There are 60 red marbles and 40 blue marbles in a bag. How many blue marbles must be added so that the probability of drawing blue is 75% ?

Question 252695: There are 60 red marbles and 40 blue marbles in a bag. How many blue marbles must be added so that the probability of drawing blue is 75% ?
Answer by richwmiller(17219) (Show Source): You can put this solution on YOUR website!
for a probability of 75%, 75% of the marbles must be blue.
3/4 must be blue
if there were 60 blue marbles the probability would be 50%
if there were 120 blue marbles it would 66.7% or 2/3
if 1/4 were red and 3/4 were blue then it would 75%
1/4x=60
x=240
240-40 is 200
so 200 more blue marbles are needed
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