Question

几道初中计算题-1/10乘11 - 1/11乘12 - 1/12乘13 .- 1/19乘20-1/2 - 1/6 - 1

Answer 1

-1/10乘11 - 1/11乘12 - 1/12乘13 .- 1/19乘20

=-(1/10-1/11+1/11-1/12+.+1/19-1/20)

=-(1/10-1/20)

=-1/2

-1/2 - 1/6 - 1/12 - 1/20 - 1/30 - 1/42

=-(1-1/2+1/2-1/3+1/3-1/4+...+1/6-1/7)

=-(1-1/7)

=-6/7