blonde poker forum

It's been a while since I've done my maths GCSE ('O' Level for the oldies), but was wondering if anyone knew how to work out this question:

If, on average, I cash in 1 in 5 and play 12 tournaments, what are the chances that I will make the money in a minimum (not exactly) of 6 events?

I gave it a crack but tied myself up in knots.

n!   Success   r!   (n-r)!   Cominations      Probability 1 combo   Probability all combos
479,001,600    6   720   720   924      1.67772E-05   0.015502148
   7   5040   120   792      4.1943E-06   0.003321889
   8   40320   24   495      1.04858E-06   0.000519045
   9   362880   6   220      2.62144E-07   5.76717E-05
   10   3628800   2   66      6.5536E-08   4.32538E-06
   11   39916800   1   12      1.6384E-08   1.96608E-07
   12   479001600      1      4.096E-09   4.096E-09

                     1.94%

Formula needed is n!/r!(n-r)! to work out your combinations and then easy from there.

Cool. Many thanks. Please excuse my stupidity, but can you confirm the values in the above formula (i.e. what does 'r' reference?)?

n!  = total number of combinations i.e. 12x11x10x9x8x7x6x5x4x3x2x1
r! = number of combinations for 6 wins i.e. 6x5x4x3x2x1
(n-r)! = number of unchosen combinations i.e. (12-6) = 6x5x4x3x2x1

The formula then gives you total combinations for posting 6 wins in 12 tournaments.  You then work out the probability of winning 6 tournies and multiply by total possible combos to get total probabilty you post 6 wins.

You then do 7 wins, 8 wins etc.

Then add them all up.

Ta. Much appreciated.