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)?
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 20121204 13:10:45 