两个因数的末尾一共有几个零，积的末尾就有几个零．… ．
28+ =90 ﹣130=240 16× =512．
×=+ =1﹣ = ÷=1．
填上合适的数： ×9=27 90﹣ =4 +12=56 56﹣ =52 21米+34米= 米 53厘米﹣41厘米= 厘米．
×==×4==1．
× =× =1× =× =1．
=
+ =1
﹣ = ÷
=1．
×
=
=
=1．
× =
× =1
× =
× =1．
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