3,492 views
3 votes
3 votes
a) 1/9

b) 2/7

c) 1/18

d) none

2 Answers

Best answer
7 votes
7 votes

In each row we have 7 pairs of squares having a common side. So, totally 8*7 = 56 such squares horizontally. Similarly, we get 56 such squares vertically. So, total number of favorable cases = 56+56=112. 
Required probability = 112/64C2
= 112*2/(64*63)

= 1/18
 

selected by
5 votes
5 votes

In 64 squares,
 4 at-corner squares, each has only 2 options to select from so    4*2C1
6*4 = 24 side squares, each has only 3 options to select from so    24*3C1
6*6 = 36 inner squares , each has 4 options to select from so    36*4C1

So.

(4 * 2 + 24 *3 + 36* 4)/(64*63) =  (224/4032) = 1/18

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