[ncray]

You can think of it this way. There are 30 spots
|__________|__________|_________|
----table 1-----table 2-----table 3

How many permutations are there where people from tables 2 and 3 end up in the first six spots?

______|_______________________
first six

For the first spot, you have 20 ppl to choose from (anyone from tables two and three). For the next spot, you have 19, then 18, 17, 16, 15. So there are 20*19*18*17*16*15 permutations of people from tables 2 and 3 filling the first six spots (in the money) out of a total 30*29*28*27*26*25. Spots 7-30 don't matter. Since 20*19*18*17*16*15/(30*29*28*27*26*25) gives you the probability of the complement (nobody from table 1 makes money), subtract it from one to get the probability that at least one person from table one makes money.