Question

计算题10*11分之1+11*12分之1+...+19*20分之一

Answer 1

1/(10*11)+1/(11*12)+...+1/(19*20)

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

=1/10-1/20

=(2-1)/20

=1/20