Question

20分之1+30分之1+42分之1+56分之1+72分之1+90分之1=?要算式!

Answer 1

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

=1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10

=1/4-1/10

=3/20