5x-20分之21=5分之7
问题描述：
5x-20分之21=5分之7
答
5x-(21/20)=7/5
5x=(28/20)+(21/20)
5x=49/20
x=49/100
答
5x-21/20=7/5
5x=7/5+21/20
=28/20+21/20
=49/20
x=49/20 除以5
=49/20乘以1/5
=49/100
=0.49
答
5x=20分之49
x =100分之49
答
x=7