x÷0.4=八分之五x÷2/5=5/8x X 5/2=5/8x=5/8X2/5x=1/4一分之四x=十五又二分之一4x=31/2x=31/2 X 1/4X=31/80.5+x=五分之六2/5+x=6/5x=6/5-2/5x=4/5x乘二分之三=十二分之五x X 3/2=5/12x=5/12 X 2/3x=5/18