一个书架有两层书，上层放的书的本数是下层的2.5倍，如果从上层取90本放入下层，则两层的书一样多。原来上层有书多少本？
直接写出得数．+=﹣=×2=×=÷3×÷3== 12×=×14=÷4=+÷+=
直接写得数+= 3+1.75=÷=×=×=﹣=+=×0+3= （+）×=×÷×=
口算下面各题．﹣=+=﹣= 2÷=×6=÷=×6=×=﹣=÷=÷=×=×=÷=÷= 6.4÷0.08= 4﹣2.92=÷=
直接写得数： 1﹣=×=÷2÷= 2×80%=+= 15÷= 35×=×÷×=
直接写出得数．﹣=×= 12×= 1÷=== 1.6×4×0.25= 0÷=
+
=
﹣
=
×2=
×
=
÷3×
= 12×
=
×14=
÷4=
+
+
+
= 3
+1.75=
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=
×
=
×
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﹣
=
+
=
×0+3=
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=
×
÷
×
﹣
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= 2÷
=
×6=
÷
=
×6=
×
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﹣
÷
=
÷
=
×
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×
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÷
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= 6.4÷0.08= 4﹣2.92=
÷
=
=
×
=
÷2÷
+
= 15÷
= 35×
=
×
÷
=
﹣
=
×
= 12×
= 1÷
=
=
= 1.6×4×0.25= 0÷
=
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