三年级口算题:整十数乘整十数 (1)70 × 40 = (2)30 × 10 = (3)30 × 10 = (4)40 × 20 = (5)60 × 50 = (6)10 × 30 = (7)20 × 70 = (8)80 × 50 = (9)30 × 70 = (10)30 × 30 = (11)40 × 60 = (12)60 × 50 = (13)70 × 80 = (14)50 × 50 = (15)90 × 60 =