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How Many?

  1. Apr 28, 2004 #1
    How Many??

    Im trying to figure this question out from an old Final exam.

    (a) In how many numbers with seven distinct digits do only the digits 1 to 9 inclusive appear (i.e. digit 0 is exluded)?

    This one i got P(9,7) because there are 9 numbers and 7 ordered places to place 7 of the 9.

    (b) How many of the numbers in (a) contain a 3 and a 6?

    For this question i got C(7,5)*P(7,7). Don't know if this is correct....

    (c) How many of the numbers in (a) contain neither a 3 nor a 6?

    This one it's either
    P(8,7) + P(8,7) - P(7,7)
    or simply
    P(7,7)

    Im pretty sure i got (a) but for (b) and (c) i need some help. Am i close?

    Thanks
     
  2. jcsd
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