3.64×0.8+6.36×0.8-3.8
=(3.64+6.36)×0.8-3.8
=10×0.8-3.8
=8-3.8
=4.2简便：12.5×2.412.5×2.4=12.5×(2+0.4)=25+5=30简便：10.1×6.8-0.6810.1×6.8-0.68=10.1×6.8-0.1×6.8=(10.1-0.1)×6.8=10×6.8=68