1x3/1+3x5/1+5x7/1+.+97x99/1+99x101/1
=(1-1/3)*1/2+(1/3-1/5)*1/2+……+（1/99-1/101）*1/2
=（1-1/3+1/3-1/5+……+1/99-1/101）*1/2
=（1-1/101）*1/2
=50/101