1. The problem statement, all variables and given/known data Suppose that |A| = n and |B| = m with n ≤ m. How many one-to-one functions f are possible with f: A → B? 2. Relevant equations If |A| = |B| = m how many different bijections f: A → B are possible? Answer: m! 3. The attempt at a solution I really do not know how to start off the question. If someone can help me get started into this equation that would be great! The relevant equation I did manage to get. but I do not know how to solve the problem when the size of A is not equal to the size of B.