2分之1比5分之1等于4分之1比x1/2*x=1/5*1/4x=(1/20)/(1/2)x=1/10
(1/2):(1/5)=(1/4):xx=(1/4)*(1/5)/(1/2)x=1/10
2/5=1/4x8x=5x=5/8
