画一个周长是12厘米的长方形，并求出它的面积．
计算下列各题，得数化成最简分数．+=+=﹣=+﹣=+=+=﹣= 1﹣﹣=
直接写出得数．+=﹣=+= 1﹣= 3+=﹣=+=﹣=
．
一个数减去，再加上．
计算，得数要约成最简分数+=﹣=﹣=+=
+
=
+
=
﹣
=
+
﹣
=
=
+
=
﹣
= 1﹣
﹣
=
+
=
﹣
=
+
= 1﹣
=
=
﹣
=
+
=
=
．
，再加上
．
+
=
﹣
=
﹣
=
+
=
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