Pick a four digit number, all digits different, such that when you add its reverse and divide it by 10, you get the number you started with.

For example: 1749+9471=11220, 11220/10 = 1122. Since 1749 is not equal to 1122, this is not the right number.

(In reply to Non-algorithmic solution by TomM)

That was great! I especially like the "First digit must be 1" reasoning. It took me a good 5 minutes to realize this must be true, since we are adding single digits, the first digit of the sum MUST be 1, and since we know we are simply dividing that sum by 10, all of the digit places (1,2,3,4) must match, with a zero in the fifth place.

Excellent, and thanks for the additional exercise in figuring out the answer BEFORE asking you a stupid question =0).

Posted by Jim C on 2003-07-07 08:22:05