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: Tricky Combinations Question

  1. Sep 7, 2011 #1
    The dean of an Engineering School invites all 9 department chairpersons and their spouses to his house for a Winter Solstice party. If each department chair may attend without a spouse, but the spouse may not attend without the department chair, how many different sets of attendees are possible?

    Anyone know the logic to set this answer up?
  2. jcsd
  3. Sep 7, 2011 #2


    User Avatar
    Science Advisor
    Homework Helper

    Try it for the case of 1 department chair. Now do 2. You can count those pretty easily. Now do you see how to get to 9?
  4. Sep 7, 2011 #3


    User Avatar
    Gold Member

    Forget about the fact that there are 9 of them, for the moment, and just focus on one chair. How many ways can the chair be represented at the event?

    EDIT: I see Dick beat me to it
  5. Sep 7, 2011 #4
    Actually, for a precaclulus math class, that can be a pretty complex problem, since for each possible set of department chairs that can show up, their corresponding spouses may or may not necessarily show up as well.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook