Answer :
9*1 = 9 9
9*2=18 1+8 = 9
each result has 2 digits ( except the first one that is only 9) add them
27 , 2+7 = 9
36, 3 +6 = 9
45, 4+5 = 9
54, 5+4 = 9
63, 6+3= 9
72, 7+2= 9
81, 8+ 1=9
The pattern is that always the sum of the digits is equal to 9.
