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


Let the number of blue balls be x.

Number of red balls = 5


Total number of balls = x + 5


P (getting a red ball) =


P (getting a blue ball) =


It is given that,


2 () =


10 (x + 5) = x2 + 5x


x2 – 5x – 50 = 0


x2 – 10x + 5x – 50 = 0


x (x – 10) + 5 (x – 10) = 0


(x – 10) (x + 5) = 0


x = 10 or x = - 5


However, the number of balls cannot be negative


Hence, number of blue balls = 10


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