a) 1 000 000 + 600 000 – 200 000 = 1 600 000 – 200 000

                                                         = 1 400 000

200 000 + 400 000 – 300 000 = 600 000 – 300 000

                                                  = 300 000

b) 20 000 000 + (4 000 + 400 000) = 20 000 000 + 404 000

                                                          = 20 404 000

1 000 000 + (90 000 – 70 000) = 1 000 000 + 20 000

                                                    = 1 020 000