一乘二分之1+ 2乘3分之1 +3乘四分之1……+2008乘2009分之一
=1-1/2+1/2-1/3+...+1/2008-1/2009
=1-1/2009
=2008/2009
3减[-5+（1减0.2除5分之3）除-2]
3-[-5+(1-0.2÷3/5)÷（-2）]
=3-[-5+(1-0.2×5/3)÷（-2）]
=3-[-5+(1-1/3)÷（-2）]
=3-[-5+2/3÷（-2）]
=3-[-5-1/3]
=3-(-16/3）
=3+16/3
=25/3