Mathematics
randirupp
25

Using the digits 3, 4, 5, 6, 7, 8, and 9, how many 7-digit numbers can be constructed if the number must begin with an odd digit and digits may not be repeated?

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(1) Answers
markleslie11

Well, there are 4 odd digits, so that's only 4 choices for the first digit.  After that, you have six digits remaining, from which you must choose 4, 6 choose 4 = 15. And there are 4! = 24 ways to arrange those 4 digits.  Altogether the number of possibilities is:  4 * 15 * 24 = 1440

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