第21题,斯认为:
设the store sold brand A为3m,则the store sold brand B为m;设gross profit of A为a,gross profit of B为b,the store paid for band A为A,the store paid for band B;则有a=(4/5)*A=3m-A(Gross profit=利润3m-成本A),b=(1/5)B=m-B。可以算出A=(5/3)*m,B=(5/6)*m,则所求(a+b)/(A+B)=60%