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Math Help - combinations

  1. #1
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    combinations

    1.How many 3 digit numbers can be made from digits 1-5 if:
    a) Repetition of digits is not allowed? 5! / (5-3)! =60

    b)Repetition of digits is allowed? I got 120 but the answer says its 125.

    c) No repetition is allowed and the number must be greater than 500? List all the numbers fitting this description.
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  2. #2
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    (b) 5*5*5 = 125

    (c) 1*4*3 = 12

    512, 513, 514, ... get the idea?
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  3. #3
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    Did you get the 4 times 3 by doing 5-1 and then multiplying it by 3 because of the 3 digit numbers?
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  4. #4
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    1st number has to be 5 ... 1 choice only

    2nd number ... 4 choices (1, 2, 3, or 4)

    3rd number ... 3 choices

    1*4*3 = 12
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  5. #5
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    Can you help me with this one

    1. List all five digit numbers that can be formed by using two 4's and three 6's.

    The answer is suppose to be...44666, 46466, 46646, 46664, 66464, 66644, 66446, 64646, 64466.

    Can you show me how I am suppose to come to that answer?
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