this question means that the total cost of purchasing flour twice in the same grain and oil store in a certain period of time is the smallest.

that is to say, the total amount purchased twice by the first method (each time buying 111 kilograms of flour) is less than that of 411 yuan by the second method (each time buying 211 yuan flour).

the breakdown is as follows:

assuming the first method is adopted, the unit price of the first flour purchase is a yuan/kg, and the second flour purchase is b yuan/kg

, so 111 * a+111 * b <; 411

means a+b <; 4 (Yuan/kg)

Answer: When the first method is adopted, the sum of the two unit prices of flour is less than 4 yuan/kg, and the first method is suitable.

The sum of the unit price of flour twice is equal to 4 yuan/kg, and the first method is suitable.

on the contrary, the second method is suitable.