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=14.52③7.25×1.8+27.5×0.18=7.25×1.8+2.75×1.8=（7.25+2.75）×1.8=10×1.8=18
