Li bought it more cost-effectively, because his eggs are the same weight, and his average price is the average of two unit prices; Li bought fewer eggs with high unit price, so his average purchase price was biased towards the one with low unit price.

I really don't understand the theoretical explanation. Give an example of good arithmetic, one is 10 yuan/kg, and the other is 20 yuan/kg. Calculate that Li is 20/ 1.5= 13.3 and Wang is 60/4= 15.