1/3+1/15+1/35+.+1/9999
=1/(1*3)+1/(3*5)+1/(5*7)+……+1/(99*101)
=1/2*[(1-1/3)+(1/3-1/5)+(1/5-1/7)……+（1/99-1/101）]
=1/2*(1-1/101)
=50/101
1/3+1/15+1/35+.+1/9999(原题）
1/3+1/15+1/35+.+1/9999
=1/(1*3)+1/(3*5)+1/(5*7)+……+1/(99*101)
=1/2*[(1-1/3)+(1/3-1/5)+(1/5-1/7)……+（1/99-1/101）]
=1/2*(1-1/101)
=50/101