Question
Sat February 23, 2013 By:

A bag contains 5 white balls and some red balls. If the probability of drawing a red ball is double that of drawing a white ball, find the number of red balls in the bag.

Expert Reply
Sat February 23, 2013
Let the number of red balls be x
 
P(drawing a white ball) = 5/(5+x)
P(drawaing a red ball) = x/(5+x)
 
Since, the probability of drawing a red ball is double that of drawing a white ball, hence
 
P(drawaing a red ball)  = 2*P(drawing a white ball)
x/(5+x) = 2*5/(5+x)
x = 10
 
There are 10 red balls in the bag. 
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