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In a bag there are 10 black & 10 white b...

In a bag there are `10` black & 10 white balls. A ball is drawn at random & 5 extra balls of same color as of drawn ball are added in the bag along with drawn ball. Now another ball is drawn and replaced in the bag but 4 balls of color same as drawn ball are removed from the bag. Again a ball drawn and found to be white find the probability that the second drawn ball was black.

A

`4/7`

B

`3/7`

C

`2/7`

D

`1/7`

Text Solution

Verified by Experts

The correct Answer is:
A

Required probability
`(1/2xx15/25xx10/21+1/2xx10/25xx15/21)/(1/2xx15/25xx10/21+1/2xx10/25xx6/21+1/2xx10/25xx15/21+1/2xx15/25xx11/21)`
`=2/(1+2/5+1+11/10)=20/(11+20+4)=4/7`
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