There is a peculiar combination of figures in this table of 9's, which,
if once noticed and perceived, will make this one of the easiest of the
tables.
9 × 2 = 18 (1 + 8 = 9)
9 × 3 = 27 (2 + 7 = 9)
9 × 4 = 36 (3 + 6 = 9)
9 × 5 = 45 (4 + 5 = 9)
9 × 6 = 54 (5 + 4 = 9)
9 × 7 = 63 (6 + 3 = 9)
9 × 8 = 72 (7 + 2 = 9)
9 × 9 = 81 (8 + 1 = 9)
9 × 10 = 90 (9 + 0 = 9)