A hint to get started
Divide by permutations of indistinguishable groups
Find the number of ways in which 6 people may be divided into groups of
(i) 1, 2 and 3,
(ii) 2, 2 and 2,
(iii) 3, 1, 1 and 1.
CJC · Discussion · Question 3
Identify which groups are distinguishable by their sizes.