I'm terrible at maths so I learned a quick way of multiplying nine when I was little using my fingers. Whatever your multiplying nine by, just bend the relevant finger. The I's represent fingers in the following explanation, the o's are the curled down fingers.
1*9= 9 oIIII IIIII = 9
2*9=18 IoIII IIIII = 18
3*9=27 IIoII IIIII = 27
Just use the Bent finger as a division between the first and second digit. After hearing that test for the first time many years ago at school, I instantly realised everyone was gonna get nine by the number work at the beginning because of the way I multiplied nines.