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Master | Next Rank: 500 Posts
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by winnerhere » Tue Aug 25, 2009 5:58 am
Two small squares(1 x 1) on a chess board are chosen at random.What is the probability that the squares thus selected share a common side

1) 1/32

2) 1/18

3) 1/8

4) 1/12

5) 1/16
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Is it A?

by enniguy » Tue Aug 25, 2009 7:02 am
Is it A? Please post the OA. If my answer is right I will post me explanation. I am not very sure.
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It's B

by enniguy » Tue Aug 25, 2009 7:16 am
Answer: B IMO.

In every row there can be 7 combination of adjacent squares. There are 8 rows. So, 8*7 = 56.

We have not considered "adjacency" vertically yet. So, in every column too, you can have 7 combination of adjacent squares. There are 8 columns. So, 56 again.

Sum = 112.
Total = 64C2 = 2016.

Probab = 112/2016 = 1/18.
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by winnerhere » Tue Aug 25, 2009 9:00 am
enniguy

ur answer is correct.

thanks for the explanation
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