First, white sugar is divided into four grades, namely refined grade, excellent grade, first grade and second grade.

At present, the prices in the market are based on the first-grade white sugar. Generally speaking, the refined grade is 6-8 yuan more expensive than the first grade, the superior grade is 3-5 yuan more expensive, and the second grade is 2-1 yuan cheaper than the first grade.

standard deviation, the cheapest is subtracted from the most expensive, because the gold grade is 6~8 yuan more expensive than the first grade, the highest value is 8 yuan, the second grade is 2~1 yuan cheaper than the first grade, and the highest grade is 1 yuan, so the standard deviation between white sugar prices is 9 yuan.