The TENor part of the name is a hint that the logic of the numbers does involve the number 10. Following the 4/2-4/5/04 Puzzle Contest in that the number of letters in the word for the number (e.g. 3 lettes in 10/ten, 4 in 5/five) we have:

If 5 (10 - 4/five = 6) + 12 (10 - 6/twelve = 4) = 10

and 7 (10 - 5/seven = 5) + 18 (10 - 8/eighteen = 2) = 7

and 8 (10 - 5/eight = 5) + 10 (10 - 3/ten = 7) = 12

what is 13 (10 - 8/thirteen = 2) + 10 (10 - 3/ten = 7) = 9

Winner: Shirley Wolf, Rockville, MD