(1)年利润=300*400/2*365/10000-1200=990万,投资收益率=990/8000*100%=12.4%
(2)售价提高10%,年利润=300*(1+10%)*400/2*365/10000-1200=1209万,投资收益率=1209/8000*100%=15.1%
售价降低10%,年利润=300*(1-10%)*400/2*365/10000-1200=771万,投资收益率=771/8000*100%=9.6%
售价降低20%,年利润=300*(1-20%)*400/2*365/10000-1200=406万,投资收益率=406/8000*100%=5.1%
