汽车上山每小时行20千米，3小时登顶，下山按原路返回，用了2小时，求汽车往返的平均速度．
直接写出得数．×=×4=×=×= 3×=÷2==×= 12=﹣1÷2=
直接写出得数．×=÷=÷26====×÷=== 1.2÷=
口算．×=÷5= 1÷= 15×= 1.25×=×4=÷= 1.8﹣40%= 12×（+）=×6+4×=
直接写出复数． ============
口算 21××0××12÷ 12÷ 1÷÷2÷×÷×．
×
=
×4=
×
×
= 3×
=
÷2=
=
×
= 12
=
﹣1÷2=
×
=
÷
÷26=
=
=
=
×
÷
=
=
= 1.2÷
=
×
=
÷5= 1÷
= 15×
= 1.25×
=
×4=
÷
= 1.8﹣40%= 12×（
+
）=
×6+4×
=
=
=
=
=
=
=
=
=
=
=
=
×0
×
×12
÷
1÷
÷2
÷
×
×
．
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