Question 252695
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