(78.6-0.786*25+0.75*21.4)除15*2001
=(0.786×100-0.786×25+75×0.214)÷15×2001
=(0.786×75+75×0.214)÷15×2001
=(0.786+0.214)×15÷15×2001
=2001
(78.6-0.786*25+0.75*21.4)除15*2001
=(0.786×100-0.786×25+75×0.214)÷15×2001
=(0.786×75+75×0.214)÷15×2001
=(0.786+0.214)×15÷15×2001
=2001