整十数加整十数的加法 (1)70 + 30 = (2)70 + 30 = (3)70 + 50 = (4)50 + 40 = (5)40 + 90 = (6)60 + 20 = (7)70 + 70 = (8)40 + 80 = (9)30 + 70 = (10)50 + 70 = (11)20 + 50 = (12)60 + 10 = (13)30 + 50 = (14)10 + 40 = (15)80 + 70 =