Permutations And Combinations Question 368

Question: The set $ S={1,2,3,…,12} $ is to be partitioned into three sets, A, B, C of equal size. Thus $ A\cup B\cup C=S,A\cap B=B\cap C=A\cap C=\phi $ . The number of ways to partition S is

Options:

A) $ \frac{12!}{{{(4!)}^{3}}} $

B) $ \frac{12!}{{{(4!)}^{4}}} $

C) $ \frac{12!}{3!{{(4!)}^{3}}} $

D) $ \frac{12!}{3!{{(4!)}^{4}}} $

Show Answer

Answer:

Correct Answer: A

Solution:

  • [a] Set $ S={1,2,3,…12} $ $ A\cup B\cup C=S,A\cap B=B\cap C=A\cap C=\phi $

$ \therefore $ The number of ways to partition $ {{=}^{12}}C_4{{\times }^{8}}C_4{{\times }^{4}}C_4 $ $ =\frac{12!}{4!8!}\times \frac{8!}{4!4!}\times \frac{4!}{4!0!}=\frac{12!}{{{(4!)}^{3}}} $