两个因数分别是72和8，积是多少？如果把因数8改成80，800，积分别是多少？你有什么发现？
直接写出得数= 1÷=÷60%=×15== 6.8÷10%= 4.5+== 2﹣==
计算 75××13×××÷××÷×÷÷÷÷÷21．
×=÷6=÷= 1÷=×=﹣=+= 6÷= 0÷=×===
直接写出得数． 18×=÷= 0.25×3.2×4= 32×（1﹣0.99）= 25%×4= 0÷=÷=×÷×=
直接写得数 72×= 1.25×8= 2.9+6.1=+=÷=×= 25÷75=÷= 1.2×= 5÷=
= 1÷
=
÷60%=
×15=
=
= 2﹣
=
=
×13
×
×
×
÷
×
×
÷
×
÷
÷
÷
÷
÷21．
×
=
÷6=
÷
= 1÷
×
=
﹣
=
+
= 6÷
=
=
=
=
=
=
÷
= 0.25×3.2×4= 32×（1﹣0.99）=
÷
×
÷
= 1.25×8= 2.9+6.1=
+
=
÷
=
×
= 25÷75=
÷
=
= 5÷
=
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