Tính bằng cách thuận tiện. a) 125 × 8 – 125 × 7 …………………………. …………………………. b) 208 × 9 – 108 × 9 ……………………… ………………………

a) 125 × 8 – 125 × 7 = 125 × (8 – 7)

                                 = 125 × 1 = 125

b) 208 × 9 – 108 × 9 = (208 – 108) × 9

                                  = 100 × 9 = 900