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.                                                                                                                  (Ans:10)

Ans: Let the number of blue balls is the bag be x

Then total number of balls is the bag = 5 + x

∴ Number of all possible outcomes = 5 + x

Number of outcomes favourable to the event of drawing a blue ball = x

(Q there are x blue balls)

∴ Probability of drawing a blue ball x/ 5 + x

Similarly, probability of drawing a red ball =  5/5 + x

According to the answer

x/5 + x = 2(5/5+x)

x = 10