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Sunday Times Teaser 2781 – Five-Card Trick

by Stephen Hogg

Published October 1 2017 (link)

I have five cards with a different digit from 1 to 5 on each. I shuffled them and placed them face-down in a row to form a concealed five-figure number. Then I invited each of my six nephews to choose a number less than fifty and they happened to choose six consecutive numbers. Then I explained that there would be a prize for anyone whose number was a factor of the concealed number. No-one was certain to win but they were all in with a chance until I revealed the final digit of the number, which ruled out two of them from winning. Then I revealed the first digit and that ruled two more out. Then I revealed the whole number and just one nephew won a prize.

What was the concealed number?

2 Comments Leave one →
  1. Brian Gladman permalink

  2. Here’s my program. I collect the numbers that can be formed by the cards into a structure that can be indexed by divisor, final digit, first digit, to make subsequent selections easier.

    This program requires the latest version of the library [ ] which includes the appropriate flattened() routine.

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