1-3分之x=0.2分之0.8-0.1x1-x/3=0.8/0.2-0.1x1-x/3=4-0.1x1-4=x/3-x/10-3=10x/30-3x/30-3=7x/30-3*30=7x-90=7xx=-90/7=-12又7分之6
