a) 4005/4007 < 1 mà 1< 1999/1997
=> 4005/4007<1999/1997
c) 1997 > 1995 ; 2101 > 2003
=> 1997.2101 > 1995.2003 hay 1997/2003 > 1005/2021
d) 2007/2005 - 1 = 2/2005
2005/2003 - 1 = 2/2003
vì 2/2005 < 2/2003 => 2007/2005 < 2003/2005
hai câu cuối k bk lm :(( sorry