=1/1*3+1/3*5+1/5*7+1/99*101
=1/2*(1-1/3)+1/2*(1/3-1/5)+1/2*(1/5-1/7)+……+1/2*(1/99-1/101)
=1/2*(1-1/3+1/3-1/5+1/5-1/7+……+1/99-1/101)
=1/2*(1-1/101)
=50/101