2008*1.2+2009*8.8=2008*1.2+2008*8.8+8.8=2008(1.2+8.8)+8.8=2008*10+8.8=20080+8.8=20088.81/6+1/12+1/20+1/30=1/2*3+1/3*4+1/4*5+1/5*6=1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6=1/2-1/6=1/3