解方程25x-14x=310x-1.8=4.310%x=4.234：25=x：4157.5：x=24：12x+5=20%x+8

Question

解方程

(2)/(5)x-(1)/(4)x=(3)/(10)	x-1.8=4.3	10%x=4.2
(3)/(4)：(2)/(5)=x：(4)/(15)	7.5：x=24：12	x+5=20%x+8

Answer 1

①(2)/(5)x-(1)/(4)x=(3)/(10)
    (8)/(20)x-(5)/(20)x=(3)/(10)
         (3)/(20)x=(3)/(10)
     (3)/(20)x×(20)/(3)=(3)/(10)×(20)/(3)
            x=2

  ②x-1.8=4.3 
x-1.8+1.8=4.3+1.8
        x=6.1

   ③10%x=4.2
0.1x÷0.1=4.2÷0.1
        x=42

④(3)/(4)：(2)/(5)=x：(4)/(15) 
     (2)/(5)x=(3)/(4)×(4)/(15)
  (2)/(5)x×(5)/(2)=(1)/(5)×(5)/(2)
      x=(1)/(2)

⑤7.5：x=24：12     
     24x=7.5×12
 24x÷24=90÷24
       x=3(3)/(4)

     ⑥x+5=20%x+8
x+5-0.2x-5=20%x+8-0.2x-5
 0.8x÷0.8=3÷0.8
         x=0.375