(9991.9991+1999.1999+1999*9991.9991)/2.0002+1001
=[1.0001*(9991+1999+1999*9991)]/2.0002+1001
=(9991+1999+1999*9991)/2+1001
=[9991*(1+1999)+1999]/2+1001
=[9991*2000+1999]/2+1001
=9991*1000+999.5+1001
=9991000+2000.5
=9993000.5