口算．30÷3= 14×5= 28×4= 43+207= 2×600= 450÷5=2400÷8= 4800÷6= 800÷4= 870﹣250= 120+200= 0÷9=
直接写出得数．== 1﹣= 4﹣=====
计算下面各题．．
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++﹣+﹣+﹣．
1﹣．
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﹣
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