1. The problem statement, all variables and given/known data Consider f:→ How many functions are there in which f^-1 is not a function? 2. Relevant equations Don't seem to fine one. 3. The attempt at a solution Try drawing the function diagram, given f:→. Then, count the total number of functions. Take too long to do so, so I quit. I just know that the inverse function must have at least an element from dom(f) to a specific element or more. For instance, f(1) = f(2) = f(3). ** EDIT ** Nevermind. I got the answer.