4-2分之1-6分之5-12分之11-20分之19
问题描述：
4-2分之1-6分之5-12分之11-20分之19
答
4-1/2-5/6-11/12-19/20
=4-(1-1/2)-(1-1/6)-(1-1/12)-(1-1/20)
=4-1+1/2-1+1/6-1+1/12-1+1/20
=1/2+1/6+1/12+1/20
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5
=1-1/5
=4/5