Puzzle of the day · No. 13 · 25 October
A number with a mistake
Schulz is selling a sofa and has put up a notice with tear-off phone numbers, but he got the number wrong: two neighbouring digits have swapped places. The number has 10 digits, all different. How many numbers will Lucky have to dial to be sure of getting through?
Answer: 9. The swap could be the first with the second, the second with the third … the ninth with the tenth: nine pairs. Since all the digits are different, each swap gives its own number.
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