The key word here is EXACTLY...

Dwarfman I think you are talking about the odds of flopping AT LEAST one pair instead of EXACTLY one pair.

So what is the odds of flopping AT LEAST one pair? Lets see that would be 1 - the probability of neither of your two cards being paired on the flop. The probability of not pairing either of your cards is (44/50)*(43/49)*(42/48), subtract that from 1 and you get 0.3242857 or 32.42857%.

Add the following percentages and see what you get:
flopping EXACTLY one pair by pairing a hole card 26.939%
flopping EXACTLY two pair by pairing a hole card AND pairing on the board 2.02%
flopping EXACTLY two pair by pairing EACH of your hole cards 2.02%
flopping EXACTLY trips by flopping two cards to one hole card 1.347%
flopping EXACTLY a full house, trips of one hole card and pairing the other 0.092%
flopping EXACTLY four of a kind, three cards to one of your hole cards 0.01%