(1)999.9+99.9+9.9+0.9
=1000-0.1+100-0.1+10-0.1+1-0.1
=1111-0.4
=1110.6
(2)2222×5.5+666.6×15
=1111(2*5.5+0.6*15)
=1111(11+9)
=1111*20
=22220
(3)4.2÷0.25÷4
=4.2×4÷4
=4.2
(4)2008×2007分之2006
=(2007+1)×2007分之2006
=2007×2006/2007+1×2006/2007
=2006+2006/2007
=2006又2006/2007