2分之1加6分之1加12分之1加20分之1加30分之1加42分之1等于几
问题描述：
2分之1加6分之1加12分之1加20分之1加30分之1加42分之1等于几
答
1/2+1/6+1/12+1/20+1/30+1/42
=1/(1*2)+1/(2*3)+1/(3*4)+1/(4*5)+1/(5*6)+1/(6*7)
=(1-1/2)+(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+(1/5-1/6)+(1/6-1/7)
=1-1/7
=6/7