Answer:13
Step-by-step explanation:
The probability of getting a pair (but NOT three of a kind) in three-card poker would be 3744/22100 = .1694+.
Obviously any of the three cards NOT in the pair is equally likely to have been dealt to you last. So in the 1/3 of cases where the non-paired card was dealt last, then your criteria were met: first you got a pair, then you got something outside the pair. 1/3 of the above value is 1248/22100 = 0.05647+.
How did I get the 3744/22100 figure?
13 (number of ranks the pair could be in) TIMES 6 (number of ways to have two of the four cards within the paired rank) TIMES 48 (number of ways to have one of the other cards outside the pair) DIVIDED BY 22100 (which is 52 choose 3, the number of unique three card poker hands.)