(2×7）分之1+（7×12）分之1+（12×17)分之1+.+(92×97）分之1
=1/5(1/2-1/7+1/7-1/2+1/12-1/17+.-1/92+1/92-1/97)
=1/5*(1/2-1*97)
=1/5*(97/194-2/194)
=1/5*95/194
=19/194