The number of one-one and onto functions that can be defined from { 1,2,3,4 } onto set  is 24  then n ( B ) is
• A
$4$
• B
$2$
• C
$3$
• D
$6$

#### Solution

Let set A be ${1,2,3,4}$.
$n(A ) = 4$.
Given that number of one to one and onto functions from A to B are 24.
If $n(B)=4$,
Number of one to one functions from A to B = $4!=24$
No of onto functions =$0$   [Since $n(A)=n(B)$]
Hence n(B)=$4$satisfies the given condition.