• # question_answer A bag contains 12 balls of two different colours, out of which x are white. One ball is drawn at random. If 6 more white balls are put in the bag, the probability of drawing a white ball now will be double to that of the previous probability of drawing a white ball. Then, the value of x is ___. A)  3                                B)  4                    C)  5                                D)  6

Correct Answer: A

Solution :

It is given that, Total number of balls = 12 Number of white balls = x $\therefore$  Probability of getting a white ball $=\frac{x}{12}$ Now, 6 white balls are added. $\therefore$ Total number of balls $=12+6=18$ Number of white balls $=x+6$ $\therefore$ Probability of getting a white ball $=\frac{x+6}{18}$ According to the question, $\frac{x+6}{18}=2\times \frac{x}{12}$ $\Rightarrow$            $x+6=3x\,\,\Rightarrow \,\,\,x=3$ $\therefore$ Number of white balls = 3

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