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Permutation and combination homework

  1. Sep 14, 2010 #1
    Find how many 3 digits odd number that can be obtained from the digit 1,2,3,4,5,6,7 if,

    1/ Repetition of digits not allowed
    2/ Repetition of digits allowed

    my work

    1/ --- the last i digit i have control 1,3,5,7

    so 2 remaining digits = 6 P 2 x 4 (4ways)

    = 120

    2/ i AM STUCK

    In fact, i don't really know whether the method is correct,i am a bit confuse, HELPPPP

    1/ 120

    2/ 196
  2. jcsd
  3. Sep 14, 2010 #2


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    For the second question, how many choices for the rightmost digit do you have?
    After that, how many choices for the middle digit? And the first? So...
  4. Sep 14, 2010 #3
    nvm i gave away too much for a hw question
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