已知a：b=4：5，b：c=0.5：，求a：b：c．
直接写得数.7.2÷9= ﹣= += ﹣+= 5﹣= ﹣×0=
= ．
直接写得数．= = = == = = =
﹣．
+= += ﹣= +=++= +﹣= ﹣﹣= ﹣+=
，求a：b：c．
﹣
= 
+
= 
﹣
+
= 5﹣
= 
﹣
= ．
= 
= 
= 
=
= 
= 
= 
=
﹣
．
+
= 
+
= 
﹣
= 
+
=
+
+
= 
+
﹣
﹣
﹣
= 
﹣
+
=
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