解
丨1/3-1/2丨+丨1/4-1/3丨+丨1/5-1/4丨+……+丨1/10-1/9丨
=(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+……+(1/9-1/10)
=1/2+(1/3-1/3)+(1/4-1/4)+……+(1/9-1/9)-1/10——内部抵消
=1/2-1/10
=2/5