设第一次价格为x元/KG,第二次价格为y元/KG.
甲:(x+y)/2
乙:1600/(800/x+800/y)=xy/(x+y)
甲减乙得:(x+y)/2-xy/(x+y)=
(x-y)^2/2(x+y)
∵x+y不等于0 ∴差≥0
答:乙合算.