a) 1 091 x 50 – 50 x 91 = (1 091 – 91) x 50

                                      = 1 000 x 50

                                      = 50 000

b) 65 x 526 + 218 x 65 + 65 x 256 = 65 x (526 + 218 + 256)

                                                        = 65 x 1 000

                                                        = 65 000

## Tính bằng cách thuận tiện:

`a) 1091 × 50 - 50 × 91`

`= 50 × (1091 - 91)`

`= 50 × 1000`

`= 50000`

`b) 65 × 526 + 218 × 65 × 256`

`= 65 × (526 + 218 × 256)`

`= 65 × (526 + 55808)`

`= 65 × 56334`

`= 3661710`