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
This question is related to TCS Interview

• May 17th, 2008

its obviously 16

• Jun 10th, 2008

there are 20 socks.of these taking 2 socks is 20C2=190.
taking right pairs is 10C2*10C2=45*45=2025.
so 2025/190=10.65 rounding to 11.
so ans is b)11.

• 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

• Dec 21st, 2010

Take a Worst case , first we take all 10 black socks only then we take two socks means it must a pair of white socks.
Ans is 12

• Jan 25th, 2011

Worst case when the 1st ten is Black socks...Then the next 2 will be white
So the ans is 12

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

Naresh Prajapati

• Jun 27th, 2015

black 10c2 and white 10c2 that means 10c2*10c2=2025/190=10.65 that take the approximately value 11.

Nikhil

• Jul 6th, 2015

Nagu

• Jul 9th, 2015

Jyoti

• Aug 12th, 2015

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

suresh

• Aug 16th, 2015

12

sandeep

• Oct 5th, 2017

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.

Vishal

• Dec 8th, 2017

a) 3