Question 1198404
<pre>
This is the number of combinations of 6 things taken 3 at a time.

{A,B,C} {A,B,D} {A,B,E} {A,B,F} {A,C,D} 
{A,C,E} {A,C,F} {A,D,E} {A,D,F} {A,E,F}
{B,C,D} {B,C,E} {B,C,F} {B,D,E} {B,D,F} 
{B,E,F} {C,D,E} {C,D,F} {C,E,F} {D,E,F} 

20 ways. The formula is {{{6C3}}}{{{""=""}}}{{{(6*5*4)/(3*2*1)}}}{{{""=""}}}{{{120/6}}}{{{""=""}}}{{{20}}}

To form the numerator, the first factor is the number we have to select from,
then the next factor is 1 less, and the next factor is 1 less than that, etc. if
necessary.  We stop when the number of factors is equal to the number we are
choosing.

To form the denominator, the first factor is the number we are choosing, and
the next factor is 1 less, and the next factor is 1 less, etc. if necessary. We
stop when we get to 1.  There should be the same number of factors in the
denominator as in the denominator.  

Form the fraction, then simplify to an integer.

Edwin</pre>