Formula:-

(I)A function is one-one function or an injection if

f(x)=f(y)

⇒ x=y for all x, y ∈ A

or f(x)f(y)

⇒ xy for all x, y ∈ A

(II)if A and B are two non-empty finite sets containing m and n

(i) Number of function from A to B = n^m

(ii) Number of one–one function from A to B

(iii) Number of one-one and onto function from A to B

(iv) Number of onto function from A to B=

Let f: A→B be one-one function

F(a)=3 and f(B)=5

Using formula

Number of one–one function from A to B

³C₅.5!=60