The last digit must be even, and only 3 of the even digits are such that you can add another digit to them and get 13. These are 4, 6 and 8, because 0 and 2 are too small. For each of the 3 ways we can choose a units digit, we can choose a tens digit only 1 way, and that's whatever digit we must add to the units digit to get 13. For each of those, there are 9 ways to choose a hundreds digit, 1-9, so as to have a three-digit number. That's 3x1x9 = 27 ways. Here they all are: 1. 158 2. 176 3. 194 4. 258 5. 276 6. 294 7. 358 8. 376 9. 394 10. 458 11. 476 12. 494 13. 558 14. 576 15. 594 16. 658 17. 676 18. 694 19. 758 20. 776 21. 794 22. 858 23. 876 24. 894 25. 958 26. 976 27. 994 Edwin