Domino Match

 Dominoes usually come in sets where the ‘highest’ domino is either the ‘double 6’ or the ‘double 9’. 

How many dominoes are there in each of these sets ? 

Choosing either of these sets as your starting point, imagine picking out two dominoes completely at random.  

The Problem :

 What is the probability that these two dominoes ‘match’ – ie the end of one matches at least one of the ends of the other ?

If we call a set of dominoes whose highest is a ‘double 6’ a ‘6-pack’, can you find the probability that any two dominoes taken from an ‘N-pack’ will match ?

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Last modified: June 18, 2007