Question 400727
Without replacement: 
{{{(r/9) * (w/8) * (b/7) = 1/21}}} ==> rwb = 24 = 2*3*4. 
Since r+w+b = 9, there 6 possibilities for the ordered triple(r,w,b):
(2,3,4)
(2,4,3)
(3,2,4)
(3,4,2)
(4,3,2)
(4,2,3)


With replacement:
{{{(r/9) * (w/9) * (b/9) = 1/21}}}==> {{{rwb = 243/7}}}, which is impossible, because r,w, b are positive integers satisfying r+ w + b = 9