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
combination sum
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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.
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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- Master | Next Rank: 500 Posts
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