A number of 50 digits has all its digits equal to 1 except the 26th digit. If the number is divisible by 13, then find the digit in the 26th place.
In my solution (see Another Approach), I lost sight of the fact that x gets added to the 1 that's already there, so the correct answer is 9, not 8.

Posted by NK
on 20040210 11:21:08 