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Counting correctly (Posted on 2015-11-19) Difficulty: 3 of 5
Find the number of 7-digit (base-10) numbers, such that each of the digits 1,2,3,4,5 must appear in the number (once or more).

Clearly, no leading zeros.

No Solution Yet Submitted by Ady TZIDON    
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re(2): analytic solution, subject to error Comment 3 of 3 |
(In reply to re: analytic solution, subject to error by Steve Herman)

Just that a brute force approach would involve 10^7 numbers to be tested for the presence of numbers that had the given digits, requiring a lot of computer time, in any of the languages I use.

Pre-analysis for a more sophisticated computer approach would lead to these 8 cases anyway, so I figured, why not go straight for an analytic approach, rather than start an analysis for a program.

  Posted by Charlie on 2015-11-19 13:31:43
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