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Probability: Permutations/Combinations

  1. Jan 17, 2012 #1
    I'm having a hard time understanding how to derive the # ways to do things.

    (a) A course has 4 sections with no limit on how many can enrol in each section. 3 students each pick a section at random.

    (i) Specify Sample Space S (64?)
    (ii)Find the probability that they all end up in the same section (3C1 /64 = 3/64??)
    (iii) Find the probability that they all end up in different sections (3P3/64 = 6/64 ??)
    (iv) Find the probability that nobody picks section 1 ( 3C2 * 2! / 64 = 6/64??)

    (b) Repeat (a) in the case where there are n sections and s students.

    Can someone please help me derive their answers of how they get the # of ways to do each. Thanks a lot!
  2. jcsd
  3. Jan 18, 2012 #2
    I suggest, first, that you check the top thread on how to present a homework problem. Or look at the standard layout used by most others.

    For your probability answer, don't forget there are 4 sections, not 3. And a little more explanation of your thinking would help others to help you.
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