销售价格为p,销售量为Q，Q=500-10(p-50) = 1000-10p = 10(100-p), p>=50
利润e = (p-40)Q = 10(100-p)(p-40)
p = 55, Q = 450, e = 6750
成本<=10000,销售量<=250, 利润e = 10(100-p)(p-40) =8000, p = 60或80，当p = 60时，Q=400>250, 所以答案是p=80,q = 200
