Частина 1. Номер 87

Обчисли зручним способом. Поясни.

380 + 269 + 120 = (380 + 120) + 269 = 500 + 269 = 769;

450 + 333 + 150 = (450 + 150) + 333 = 600 + 333 = 933;

160 + 187 – 60 = (160 – 60) + 187 = 100 + 187 = 287;

170 + 279 – 70 = (170 – 70) + 279 = 100 + 279 = 379;

434 – 70 – 34 = (434 – 34) – 70 = 400 – 70 = 330;

868 – 90 + 68 = (868 + 68) – 90 = 936 – 90 = 846.