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: Intro Statistics combination/probability problems.

  1. Feb 23, 2012 #1
    Hello. Am I counting right with these problems? I can't remember exactly how they were worded, but I remember what they were asking...

    1) Given 20 men and 20 women, how many groups of 12 can you make with 6 men and 6 women.

    I said 20.Combination.6 * 20.Combination.6.

    2) given S= {1, 2, 4, 5, 7}, you will choose 3 randomly from the set. What's the probability of getting an even number greater than 500?

    I said 12 / 5.Permutation.3.

    How I got 12:

    1. 3 ways of having 5 first, 2 last.
    2. 3 ways of having 5 first, 4 last.
    3. 3 ways of having 7 first, 2 last.
    4. 3 ways of having 7 first, 4 last.

    Added it up to get 12. I then divided it by a permutation because order is important?...


    3) What is the probability that two randomly chosen people were both not born in June?

    I said P(First not born in June ^ Second not born in June)= (11/12) * (11/12)



    Is my counting right? Thanks for your help.
     
  2. jcsd
  3. Feb 23, 2012 #2

    Ray Vickson

    User Avatar
    Science Advisor
    Homework Helper

    You counting for (2) is incorrect. If you first pick 5, then picking any two other numbers gives you a result > 500. If you first pick 7, then picking any two other numbers gives you a result > 500. If you pick anything other than 5 or 7 first you will not get a result > 500.

    RGV
     
  4. Feb 24, 2012 #3
    @Ray Vickson,

    Thanks for your help.

    For number 2, they have to be even and >500, how do I go about solving that part?
     
  5. Feb 24, 2012 #4

    Ray Vickson

    User Avatar
    Science Advisor
    Homework Helper

    Surely you know what an even number looks like!

    RGV
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook