解方程或解比例.12x+23x=0.5 &nbs...

解方程或解比例.12x+23x=0.5 x:7.5=0.3:9.

(1)
1
2
x+
2
3
x=0.5,
      (
1
2
+
2
3
)x=0.5,
            
7
6
x=
1
2

        
7
6
7
6
=
1
2
÷
7
6

               x=
3
7


(2)x:7.5=0.3:9,
         9x=7.5×0.3,
         9x=2.25,
      9x÷9=2.25÷9,
          x=0.25.
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