-27
10 and -9
-1
If the digit sum of a number adds up to 9 then it is divisible by 9.
-91
9 and 11.
-3 and -3.
-10 and 1
5 & 9. 5 + 9 = 14... 5 x 9 = 45.
First it adds by 3. Then on 4, 8, 12 it adds by 4. On 5 and 10 it adds by 5. So i guess it is 3, 4, 5.
-41
-19