Here's the way the coin flip works.

If we flip a coin twice we can get 4 outcomes:
2 heads probability .5*.5 = .25
2 tails .5*.5 = .25
1 heads 1 tails = .5*.5 = .25
1 tails 1 heads = .5*.5 = .25

3 of these outcomes gives us our required 1 head result. So the odds of getting at least 1 head out of 2 coin tosses is:

.25+.25+.25 = .75 = 75%

In our pocket pair/trips example we have the following possible results for the 3 flop cards, excluding the possibilities with 2 3rd cards because they would give us 4 of a kind (3rd card = the card that completes the 3 of a kind):

1=other 2=other 3=other Prob=.96*.96*.96 = .885
1=3rd 2=other 3=other Prob= .04*.96*.96= .037
1=other 2=3rd 3=other Prob = .037
1=other 2=other 3=3rd Prob = .037

Total = 3.7%+3.7%+3.7% = 11.1%

This gets me closer to the 10.8% from the web site.

Thanks for the example of the coin toss to stimulate my thinking. Perhaps one of the experts here can fill in the last few blanks to correct my errors.

Thanks to all for your help.

Eric