Mistake in Harringtons second edition??

I am not sure what forum to put this in, but since it applies to super satellite play, ill try this one.

I think I found a formula error in Harrington's second edition p 422. I believe his formula is a "close" aproximation for this case and many others, but suppose we change the problem slightly and say instead of 6 people left there are only 5, but one of them has 9000 in chips. His equation would then read

x + x + 4.5x + 4.5x + 9.0x = 400.

x would still equal 20, but now our 9000 chip player would have 180% chance of qualifying. This of course can't be. So did i make a mistake, or is this an old problem that has been solved, or does anybody know the proper formula, (assuming all are equal skill levels)? I have some ideas of a formula, but it is somewhat complicated and I wanted to know if the problem has already been solved, (or I am missing something here),

Thanks,
Puppy Toes