Вправи 601 - 674 » 611-612

611. 860 + 40 = 900; 900 – 50 = 850; 630 + 70 = 700; 1000 – 80 + 70 = 990. 612. (280 – 240) : 8 = 40 : 8 = 5; 800 – (701 – 1) = 800 – 700 = 100; (120 – 90) : 6 = 30 : 6 = 5; 200 + (699 + 1) = 200 + 700 = 900; 560 + 40 – 400 = 600 – 400 = 200; 870 + (110 – 80) = 870 + 30 = 900.