巧算:2003÷2004×2005
2003/2004*2005
=(2003*2005)/2004
=(2004+1)*(2004-1)/2004
=(2004^2-1^2)/2004
=2004^2/2004-1/2004
=2004-1/2004
=2003又2003/2004
2003/2004*2005
=(2003*2005)/2004
=(2004+1)*(2004-1)/2004
=(2004^2-1^2)/2004
=2004^2/2004-1/2004
=2004-1/2004
=2003又2003/2004