1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Combinatorics Help! Tricky problem here!

  1. Sep 26, 2012 #1
    1. The problem statement, all variables and given/known data

    Consider f:[7]→[9]

    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:[7]→[9]. 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.
    Last edited: Sep 26, 2012
  2. jcsd
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted