Номер 365

290 – 40 – 40 = (200 + 90) – 40 – 40 = 200 + (90 – 40 – 40) = 200 + 10 = 210;
(630 – 400) + 50 = (600 + 30) – 400 + 50 = (600 – 400) + (30 + 50) = 200 + 80 = 280;
450 – (20 + 30) = (400 + 50) – 50 = 400 + (50 – 50) = 400 + 0 = 400;
690 – (50 + 20) = (600 + 90) – 70 = 600 + (90 – 70) = 600 + 20 = 620;
870 – 40 – 200 = (800 + 70) – 40 – 200 = (800 – 200) + (70 – 40) = 600 + 30 = 630;
720 – 20 + 200 = 700 + 200 = 900.