Tính bằng cách thuận tiện.

a) 67 × 3 + 67 × 7

b) 45 × 6 + 45 × 4

c) 27 × 6 + 73 × 6

a) 67 × 3 + 67 × 7 = 67 × (3 + 7)

                              = 67 × 10

                              = 670

b) 45 × 6 + 45 × 4 = 45 × (6 + 4)

                              = 45 × 10

                              = 450

c) 27 × 6 + 73 × 6 = (27 + 73) × 6

                              = 100 × 6

                              = 600