解方程. 4:x=3:2.4 x+x=9 4x﹣3.6=3.6 1﹣20%x= 4.2:x="0.7×14" =
(1–×)÷ [(1–)×]÷4
[(1–)×]÷4 ++
(–)÷(+) [1–(+)]÷3.5