1/3*5+1/5*7+…+1/2001*2003
=1/2(1/3-1/5)+1/2(1/5-1/7)+…+1/2(1/2001-1/2003)
=1/2(1/3-1/5+1/5-1/7+…+1/2001-1/2003)
=1/2(1/3-1/2003)
=1/2*(2000/6009)
=1000/6009
1/3*5+1/5*7+…+1/2001*2003
=1/2(1/3-1/5)+1/2(1/5-1/7)+…+1/2(1/2001-1/2003)
=1/2(1/3-1/5+1/5-1/7+…+1/2001-1/2003)
=1/2(1/3-1/2003)
=1/2*(2000/6009)
=1000/6009