求"4-2分之1-6分之5-12分之11-20分之19"的简便运算

4-2分之1-6分之5-12分之11-20分之19"的简便运算解,得：4-(1/2)-(5/6)-(11/12)-(19/20)==4-[1-(1/2)]-[1-(1/6)]-[1-(1/12)]-[1-(1/20)]==4-1-1-1-1+(1/2)+(1/6)+(1/12)+(1/20)==1/2+1/6+1/12+1/20==1-1/2+(1/2-1/3)+(...