Question

分数的简便计算,急,明天要交!7 13 21 31 43 57 73 91— +— +— +— +—+ —+ — +—6

Answer 1

1+1/6+1+1/12+1+1/20+1+1/42+1+1/56+1+1/72+1+1/90

=8+(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+(1/5-1/6)+(1/6-1/7)+(1/7-1/8)+(1/8-1/9)+(1/9-1/10)

=8+1/2-1/10

=8.4