x:1/4=1/2:3/10
x×3/10=1/4×1/2
x×3/10=1/8
x=1/8×10/3
x=5/121.5比4.5等于X比二分之一1.5:4.5=x:1/21.5×0.5=4.5x4.5x=0.75x=1/6