简便计算0.8×2/11+4.8×（-2/7）-2.2×2/7+0.8×9/11=0.8×（2/11+9/11）-（4.8+2.2）×2/7=0.8×1-7×2/7=0.8-2=-1.2
=0.8×2/11-4.8×3/7-2.2×3/7+0.8×9/11=0.8×（2/11+9/11）-3/7×（4.8+2.2）=0.8×1-3/7×7=0.8-3=-2.2
