650 + 30;
780 − 70;
240 − 20;
40 * 4;
80 * 7;
90 * 6;
640 : 8;
540 : 9;
270 : 3;
130 * 5;
150 * 4;
750 : 3.
650 + 30 = 680;
780 − 70 = 710;
240 − 20 = 220;
40 * 4 = 160;
80 * 7 = 560;
90 * 6 = 540;
640 : 8 = 80;
540 : 9 = 60;
270 : 3 = 90;
130 * 5 = (100 + 30) * 5 = 100 * 5 + 30 * 5 = 500 + 150 = 650;
150 * 4 = (100 + 50) * 4 = 100 * 4 + 50 * 4 = 400 + 200 = 600;
750 : 3 = (600 + 150) : 3 = 600 : 3 + 150 : 3 = 200 + 50 = 250.