1/12+1/20+1/30+1/42+.+1/9900
=1/(3*4)+1/(4*5)+1(5*6)+...+1/(99*100)
=1/3-1/4+1/4-1/5+1/5-1/6+...+1/98-1/99+1/99-1/100
=1/3-1/100
=97/300