有一张等腰直角三角形的纸（如图1），AB=20厘米．把它的两个角向斜边的中点O折叠，使A、B两点都与O点重合（如图2），再以CO为对称轴将图2对折，得到一个梯形（如图3）．求这个梯形的面积．
直接写得数+=﹣=×=×5= 2﹣= 3÷7=÷=÷4=
直接写出得数．+﹣×6×24× 5÷4.8 （+）×6 9×0+（+）÷ 12×11×× 1.5﹣+﹣．
直接写出得数． 1÷= 1﹣﹣=×==×12=（3+）×0=÷=+=
计算：﹣= 18×===×12=÷2=+=﹣=
===================== 2.5×16======== 1.5÷0.05== 1.5÷0.05==== 2.5×0.4============ 6.25+1.75===============
+
=
﹣
=
×
=
×5=
= 3÷7=
÷
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÷4=
+
﹣
×6
×24
×
5
÷4.8
+
）×6 9
×0+
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+
12×11×
×
1.5﹣
﹣
．
= 1﹣
﹣
×
=
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×12=（3
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÷
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+
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﹣
= 18×
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×12=
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﹣
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= 2.5×16=
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= 1.5÷0.05=
= 1.5÷0.05=
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= 2.5×0.4=
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= 6.25+1.75=
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