Question

Write the total number of one-one functions from set A = {1, 2, 3, 4} to set B = {a, b, c}.

Answer 1

A has 4 elements and B has 3 elements.
Also, one-one function is only possible from A to B if $n\left(A\right)\le n\left(B\right)$.
But, here $n\left(A\right)>n\left(B\right)$.
So, the number of one-one functions from A to B is 0.