## Problem of the Week 1103## Missing Digit
- Alice: Pick a 5-digit number.
- Bob: Got it.
- Alice: Now reverse it and subtract it from the original.
- Bob: Done.
- Alice: Now pick one of the five digits of the result and circle it (but don't choose a zero). Tell me the other four digits, in some random order.
- Bob: Sure; they are 1, 1, 0, and 8.
- Alice: Then the circled digit is....
Alice does indeed correctly give the circled digit. How did she do it? Suggested by Bill Owens, Macalester '01. © Copyright 2008 Stan Wagon. Reproduced with permission. |

15 September 2008