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Two Dominoes (Posted on 2012-12-04) Difficulty: 2 of 5
What is the probability that two dominoes drawn randomly from a standard set of 28 bones will match (i.e. will share the same number of pips, thus allowing concatenation)?

No Solution Yet Submitted by Ady TZIDON    
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Solution Solution Comment 1 of 1
The first domino is either a doubles (7/28) or two different numbers (21/28)

If the first is doubles there are only 6 others that will match it.
[00 matches 01, 02, 03, 04, 05, 06]

If the first is not doubles there are 12 others that match it.
[01 matches 00, 02, 03, 04, 05, 06, 11, 12, 13, 14, 15, 16]

Total probability is (7/28)*(6/27) + (21/28)*(12/27) = 254/756 = 7/18

  Posted by Jer on 2012-12-04 13:10:45
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