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Math Help - Question on counting methods/multiplication of choices i'm not sure which it is

  1. #1
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    Question on counting methods/multiplication of choices i'm not sure which it is

    A 4-digit code is to be formed using the numbers 0, 1, 2, . , 8, 9. How many
    different code formations are possible if the first digit must be more than 7 and
    repetition of numbers is NOT allowed?

    Is the first step 2! ?
    I really have no idea how to do this question.
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  2. #2
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    Quote Originally Posted by mngeow View Post
    A 4-digit code is to be formed using the numbers 0, 1, 2, . , 8, 9. How many
    different code formations are possible if the first digit must be more than 7 and
    repetition of numbers is NOT allowed?

    Is the first step 2! ?
    I really have no idea how to do this question.
    Two possibilities for first digit. After you fix first digit, 9 possibilities for second digit. After you fix first two digits, 8 possibilities for third digit...

    So in all it's 2 * 9 * 8 * 7.
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  3. #3
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    ooh.I get it now.Thanks alot
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