Nines are easy. Up to 9 × 9 (only using integers) you can use this system: subtract 1 from whatever number your multiplying 9 by and that will give you your first digit. Then take whatever number needs to be added to the first digit to sum to 9, and that is your second digit. Ex: 9 × 7 and 7 – 1 = 6 and 9 – 6 = 3 so then 9 × 7 = 63! After that, 10 x anything is easy, and so is 11 time any integer below 11. Just remember that 12 × 9 is 108 and you good!
Nines are easy. Up to 9 × 9 (only using integers) you can use this system: subtract 1 from whatever number your multiplying 9 by and that will give you your first digit. Then take whatever number needs to be added to the first digit to sum to 9, and that is your second digit. Ex: 9 × 7 and 7 – 1 = 6 and 9 – 6 = 3 so then 9 × 7 = 63! After that, 10 x anything is easy, and so is 11 time any integer below 11. Just remember that 12 × 9 is 108 and you good!