二年级口算题:尾数是0三位数加减法 (1)310 + 690 = (2)830 + 610 = (3)930 + 210 = (4)440 + 720 = (5)290 - 210 = (6)590 - 410 = (7)270 - 140 = (8)650 - 190 = (9)840 - 730 = (10)340 + 360 = (11)920 - 530 = (12)580 + 400 = (13)540 - 220 = (14)350 - 260 = (15)550 - 440 =