脱式计算.能简算的要简算.注意能简算的要简算!

①486-450÷18×12 ②0.63÷[﹙1-0.625﹚×8]
=486-25×12 =0.63÷﹙0.375×8﹚
=486-300 =0.63÷3
=186 =0.21
③2008÷（2008+2008/2009)+1/2010
=2008÷2008+2008÷（2008/2009）+1/2010
=1+2009+1/2010
=2010+1/2010
④(8+4/9)÷4×(18/19)
=(8÷4+4/9)÷4×(18/19)
=(2+1/9)×(18/19)
=(19/9)×(18/19)
=2