Tính nhẩm9 x 1 = .....9 x 2 = .....9 x 3 = .....9 x 4 = .....1 x 9 = .....2 x 9 = .....3 x 9 = .....4 x 9 = .....9 x 5 = .....9 x 6 = .....9 x 7 = .....9 x 8 = .....5 x 9 = .....6 x 9 = .....7 x 9 = .....8 x 9 = .....