①3.5%×9.9
=0.035×（10-0.1）
=0.035×10-0.035×1
=0.35-0.035
=0.315                   
②4.62+9.9
=4.62+10-0.1
=14.62-0.1
=14.52
③7.25×1.8+27.5×0.18
=7.25×1.8+2.75×1.8
=（7.25+2.75）×1.8
=10×1.8
=18