估算 39×19≈ 798×60≈ 301×102≈ 201×51≈ 399×42≈
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1--
口算。+= -= += - +=0.63×1000= 0. 75-0.25= 0.07+0.03= 0. 9÷0.03= 0.4×0.8=
×= ÷3=÷= -=3÷15= +0.25=1÷= 85%-15%=10÷10%= 5×÷5×=
脱式计算下面各题。4÷-0.6 ×÷(+)÷ ÷[1÷(-)]