3.5X+1.8=12.30.8X-4=1.65X÷2=10X-0.25X=3X+25X=2145X+25X=12

Question

3.5X+1.8=12.3	0.8X-4=1.6
5X÷2=10	X-0.25X=3
X+(2)/(5)X=21	(4)/(5)X+(2)/(5)X=(1)/(2)

Answer 1

①3.5X+1.8=12.3
 3.5X+1.8-1.8=12.3-1.8
         3.5X=10.5
    3.5X÷3.5=10.5÷3.5
            X=3；
 ②0.8X-4=1.6
 0.8X-4+4=1.6+4
     0.8X=5.6
0.8X÷0.8=5.6÷0.8
        X=7；

③5X÷2=10
  (5)/(2)X×(2)/(5)=10×(2)/(5)
      X=4
  ④X-0.25X=3
      0.75X=8
0.75X÷0.75=8÷0.75
          X=10(2)/(3)；

   ⑤X+(2)/(5)X=21
     1.4X=21
1.4X÷1.4=21÷1.4
        X=15
 ⑥(4)/(5)X+(2)/(5)X=(1)/(2)

(6)/(5)X=(1)/(2)
    (6)/(5)X×(5)/(6)=(1)/(2)×(5)/(6)
        X=(5)/(12)；