In how many different ways can a set of 3n elements be partitioned into 3 subsets of equal number of elements?
Isn't this case of distributing distinguishable objects and distinguishable boxes, so the answer should be $(3n)! / ((n!)^3 )$.
But answer given is $ (3n)! / (6*(n!)^3) $
Can anybody explain? Or post a link where to study all concepts of permutation and combination and counting