Question 496853
There are 21 choices for the 1st person
There are 20 choices for the 2nd person
There are 19 choices for the 3rd person
and so on, until
There is 1 choice for the 21st person
This is a string of AND's not OR's
( any 1 of 21) AND ( any 1 of 20) AND ( any 1 of 19 ) etc.
When choices are ANDed, you multiply the possibilities
{{{ 21*20*19*18*17*16*15*14*13*12*11*10*9*8*7*6*5*4*3*2*1 }}}
This maxed out my little Staples 8 digit calculator. It
also equals {{{ 21! }}}