RD SHARMA

Question

There are 4 white and 4 black balls in a bag and 3 balls are drawn at random.If balls of same colour are identical,the probability that none of them are black is,(I am getting 1/14,ans is 1/4)

Answer 1

1/4 is correct. They are saying that balls are identical.

Now, I will tell your mistake so that you understand.

You did 4C3 / 8C3.

Now, if you are doing 4C3 means all 4 white balls are different. That shouldnt be the case. You can choose 3 white balls in only 1 way

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Sample space

= 0 white, 3 black

OR 1white, 2 black

OR 2 white, 1 black

OR 3 white, 0 black

= 4 ways

Favorable events = 3 white, 0 black = 1 way

Thus, req probablity = 1/4