1-2+3-4+5-6+.+2005-2006+2007 =(1-2)+(3-4)+(5-6)+.+(2005-2006)+2007 =-1-1-1-1-1……-1+2007 =-（2006/2）+2007 =1004 1.3/7 × 49/9 - 4/3 2.8/9 × 15/36 + 1/27 3.12× 5/6 – 2/9 ×3 4.8× 5/4 + 1/4 5.6÷ ...