Tính bằng cách thuận tiện.

a) 48 × 9 – 48 × 8                                                    b) 156 × 7 – 156 × 2

a) 48 × 9 – 48 × 8 = 48 × (9 – 8)

                              = 48 × 1

                              = 48

b) 156 × 7 – 156 × 2 = 156 × (7 – 2)

                                 = 156 × 5

                                 = 780