Question

1/12(是12分之1)+1/20+1/30+1/42+1/56+1/72+1/90的简便做法（等于7/307分之30）

Answer 1

1/12(是12分之1)+1/20+1/30+1/42+1/56+1/72+1/90

=1/(3*4)+1/(4*5)+...+1/(9*10)

=1/3-1/4+1/4-1/5+...+1/9-1/10

=1/3-1/10

=7/30