首先声明,我推荐的解法是【解法2】,解法2比较容易,计算量比解法1少太多太多了.

五分之一 我就写成1/5 了哦,分子在前,分母在后.

【解法1】
|1/5-150/557 |+| 150/557-1/2 |-1/2
=| 557/2785-750/2785 |+| 300/1114-557/1114 |-1/2
=193/2785+257/1114-1/2
=386/5570+1285/5570-1/2
=1671/5570-2785/5570
= -1114/5570
= -1/5

上面是按部就班的方法,非常麻烦,其实观察一下式子能看出来点儿规律
|1/5-150/557 |+| 150/557-1/2 |-1/2
=| 557/2785-750/2785 |+| 300/1114-557/1114 |-1/2
写到这步就可以确定式子内部的符号了,然后别计算,直接根据里面正负号去绝对值符号
【解法2】
|1/5-150/557 |+| 150/557-1/2 |-1/2
= | 557/2785-750/2785 |+| 300/1114-557/1114 |-1/2
= -(1/5-150/557 )-(150/557-1/2)-1/2
= 150/557 -1/5-150/557+1/2 -1/2
=-1/5