isi-entrance 2012 Q6

isi-entrance · India · solved Permutations & Arrangements Permutation Properties and Enumeration (Abstract)

Let $f:\{1,2,3,4\} \to \{1,2,3,4\}$ be a function such that $f(i) \neq i$ for all $i$ (i.e., a derangement). Find the number of such functions.

The sample space gives 12 such functions. (C)

Let $f:\{1,2,3,4\} \to \{1,2,3,4\}$ be a function such that $f(i) \neq i$ for all $i$ (i.e., a derangement). Find the number of such functions.