Вправи: 49

49. Обчисли зручним для тебе способом.

350 + 470 = 350 + 50 + 420 = 400 + 420 = 820;

900 – 70 = 800 + 100 – 70 = 800 + 30 = 830;

3400 + 270 = 3400 + 200 + 70 = 3600 + 70 = 3670;

280 – 190 = 280 – 200 + 10 = 80 + 10 = 90;

260 + 80 = 260 + 40 + 40 = 300 + 40 = 340;

4300 – 340 = 4300 – 300 – 40 = 4000 – 40 = 3960;

320 • 4 = 300 • 4 + 20 • 4 = 1200 + 80 = 1280;

960 : 40 = 800 : 40 + 160 : 40 = 20 + 4 = 24;

720 : 12 = 720 : 2 : 6 = 360 : 6 = 60;

510 : 3 = 300 : 3 + 210 : 3 = 100 + 70 = 170;

9 • 130 = 130 • 10 – 130 = 1300 – 130 = 1170;

810 : 30 = 810 : 10 : 3 = 81 : 3 = 60 : 3 + 21 : 3 = 20 + 7 = 27.