解：采用分配律，原式=2.8-2.8x0.11=2.8x（1-0.11）=2.8x0.89=（3-0.2）x0.89=3x0.89-0.2x0.89=2.67-0.178=2.492
2.8-2.8×0.1=2.8-0.28=2.8-0.2-0.08=2.6-0.08=2.52
2.8-2.8*0.1=2.8*（1-0.1）=2.8*0.9=2.52
