Question

6分之1加12分之1加20分之一加42分之1加56分之1加72分之1加90分之1，等于多少

Answer 1

1/6+1/12+1/20+1/42+1/56+1/72+1/90
=(2+1)/12+(21+10+7.5)/420+(10+8)/720
=1/4+11/120+1/40
=(30+11+3)/120
=44/120
=11/30

Answer 2

=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
=2/5

Answer 3

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

=1/(2*3)+1/(3*4)+1/(4*5)+……+1/(9*10)
=1/2-1/3+1/3-1/4+1/4-1/5+……+1/9-1/10
=1/2-1/10
=2/5