Question

What is the probability that two squares selected on a chessboard have a common side?

Answer 1

Answer:

The right answer is  1/18.  

Here is how to solve:  

In 64 squares, there are:  

(1) 4 at-corner squares, each has ONLY 2 squares each having a side in common with...  

(2) 6*4 = 24 side squares, each has ONLY 3 squares such that each has a side in common with...  

(3) 6*6 = 36 inner squares, each has 4 squares such that each has a side in common with...  

So we have the calculation:  

P = (4/64)*(2/63) + (24/64)*(3/63)+ (36/64)*(4/63)  

P = 1/18  

Hope this help  

Step-by-step explanation:

Answer 2

simple common side squares 7*8+7*8=112 favourable outcome s.
total ways of selecting any two square s = 63*16
therefore propability=1/18