口算300×2= 600×7= 1000×4= 999×0= 20+19=50+45= 225+43= 79﹣52= 3+73= 49×7=
计算下列各题．==．
直接写出得数．== 1﹣ 2.4+===
直接写出得数． 4x+6x= 10﹣﹣= 1﹣=﹣=+=+=﹣= x+3x+7x=+= 1﹣﹣=﹣=+=
计算下面各题，能简便的要简便．++++ 4﹣﹣ 78﹣8.5+22﹣0.5﹣（+）﹣++．
直接写出得数．==========
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