PROBLEM 116
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Midshipman Bob invites Joe to see his new program, 
which prints 2 x 2 matrices with random integer entries.  
(These entries are as likely to be even as to be odd.)  
Joe, being a bit of a gambler, wants to bet Bob a dollar 
that the next matrix will have an even determinant.  
Should Bob take the bet?  
What is the probability that the next matrix will have an even determinant?

Note:  
The determinant of the 2 x 2  matrix

    |a  b|
A = |    |
    |c  d|

is given by  det(A) = ad - bc.

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ADVANCED PROBLEM 116A
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What is the probability that the determinant of an  n x n   matrix 
with randomly chosen integer entries is divisible by the prime number  p.  
(Assume that the residues  0, 1, 2, ... , p-1  are equally likely 
for each integer entry.)