Question 587136
A) 
5+3+2=10
5/10 = 1/2  the probability of drawing a white ball.
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B) 
(5+x)/(10+x) = 3/4
5+x = 3(10+x)/4
5+x=(30+3x)/4
20+4x=30+3x
x=10  white balls must be added to the box so that the probability of drawing a white ball is 3/4
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C) Similar to B
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Ed