4/7X=20/21
x=20/21÷4/7
x=5/3
1/2X---1/4X=3/8
1/4x=3/8
x=3/8÷1/4
x=3/2
,(1---50%)X=1/4
0.5x=0.25
x=0.25÷0.5
x=0.5