Probability

4) There are 5 distinct pairs of white socks and 5 pairs of black socks in a cupboard. In the dark, how many socks do I have to pull out to ensure that I have at least 1 correct pair of white socks? a) 3 b) 11 c) 12 d) 16
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anon1987

  • Dec 7th, 2009
 

It will be 12, there is total of 20 socks,
At the worst case you have chosen 10 sock i:e 10 attempts ,
To get a pair of white socks you need 2 choose 2 more socks which must be 2 for making a white pair.

That is the total of (10 +2 ) attempts are needed

Ans: 12

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Abhishek

  • Jun 11th, 2015
 

Only 3 socks you have to take because any 3 will consists of 1 black, 2 white or 2 black, 1 white. 2 same color means 1 pair

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Naresh Prajapati

  • Jun 27th, 2015
 

Answer is B. 20c2=20*19/2=190
black 10c2 and white 10c2 that means 10c2*10c2=2025/190=10.65 that take the approximately value 11.

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Nikhil

  • Jul 6th, 2015
 

Answer is c) 12

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Nagu

  • Jul 9th, 2015
 

12 is the answer

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Jyoti

  • Aug 12th, 2015
 

3 socks have to pick out to make pair of white socks.

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suresh

  • Aug 16th, 2015
 

12

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sandeep

  • Oct 5th, 2017
 

The answer is 11
5 white pairs =10 socks ,pick 5 from them which do not match with any other for worst case

5 black pairs =10 socks ,pick 5 from them which do not match with any other for worst case

Now when you will pick the next sock of any color it will automatically matches with one of the ten socks you have picked earlier.

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Vishal

  • Dec 8th, 2017
 

a) 3

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