Don’t you hate math?
“Hi–You write: ‘Note that the final, jumbled-up three digits can’t divide EXACTLY by 9 (giving remainder zero), because then so would my “N,” which would mean you hadn’t removed a digit….’ Actually, If your removed digit is a nine, then the ‘final, jumbled-up three digits’ will still be divisible by nine.
“But the method still gives the right result. (9-0 = 9, the removed digit.)
“That’s why they forbid you to remove a zero; without that rule, the method can’t distinguish whether you remove a nine or a zero.”
[Derb] The reader is quite correct. By spotting my error, however, he has FORFEITED HIS CHANCE TO WIN THE MUCH-COVETED PRIZE.