Let A and B be any two sets such that n(A) = p and n(B) = q,

n(A) = p, n(B) = q.

here any element of set A, can be connected with elements of B in q ways. 


and there are p such elements in A. 

$\therefore$ Total function possible is $\frac{q \times q \times q \ldots \ldots \times q}{p \text { times }}$

i.e $q^{p}$

$\therefore$ Total functions from $A$ to $B q^{p}$ i.e $n(B)^{n(A)}$.