Question
A box contains 24 identical balls of which 12 are white and 12 black. The balls are drawn at random from the box one at a time with replacement. The probability that a white ball is drawn for the 4th time on the 7th draw is
Answer: Option C
:
C
In any trail, P(getting white ball) = 12
P(getting black ball) = 12
Now, required event will occur if in the first six trails 3 white balls are drawn in any one of the 3 trails from six. The remaining 3 trails must be kept reserved for black balls. This can happen
In 6C3×3C3=20 ways.
=20×(12)3×(12)3×12=532
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:
C
In any trail, P(getting white ball) = 12
P(getting black ball) = 12
Now, required event will occur if in the first six trails 3 white balls are drawn in any one of the 3 trails from six. The remaining 3 trails must be kept reserved for black balls. This can happen
In 6C3×3C3=20 ways.
=20×(12)3×(12)3×12=532
Was this answer helpful ?
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