If a set P contains 5 elements and the set Q contains 8 elements, then the number of one-one functions from A to B is :

${ }^8 C_5 \times 5$ !

No. of elements in P = p = 5

No. of elements in Q = q = 8

p → contains m elements

q → contains n elements

then no. of one one functions from p → q

$\equiv { }^n P_m = { }^n C_m \times m$ !

No of one one fractions from P → Q is ${ }^8 P_5={ }^8 C_5 \times 5$ !