Let x denote the total number of one –one functions from a set A with 3 elements to a set B with 5 elements and y denotes the total number of one – one function from the set A to be set  $A\times B$ then: 

x denotes total no of 1 – 1 function from A to B and n(A) = 3;  n(B) = 5

            x =${ }^5{P}_3=5\times 4\times 3=60$

            Y denotes total number of one to one function from A to A x B and $n\left(A\right)=3,n(A\times B)\text{}=15$

            And $y{=}^{15}{P}_3=15\times 14\times 13=2730$

$\frac{y}{x}=\frac{2730}{60}=\frac{91}{2}\Rightarrow 2y=91x$