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+3 votes
1.4k views
a) 1/9

b) 2/7

c) 1/18

d) none
asked in Probability by Junior (645 points) | 1.4k views

2 Answers

+6 votes
Best answer

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
 

answered by Boss (18k points)
selected by
+3 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

answered by (125 points)


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