Question

6分之一加12分之一加20分之一加30分之一加42分之一加56分之一加72分之一加90分之一等于多少?

Answer 1

1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90

=(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)

=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

=1/2-1/10

=4/10

=2/5