10th Class Mathematics Probability Question Bank Probability

  • 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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