Mathematical problems of inequality group The price and quantity of goods bought by the two stores are the same. Store a: after purchasing 200 yuan goods, you can apply for a 20% discount card, and later you can enjoy a 20% discount when purchasing goods; store B can apply for a 10% discount card when purchasing 100 yuan goods, and later you can enjoy a 10% discount when purchasing goods At the beginning, we need to use the system of inequalities to solve the problem, not to discuss it by classification,
Let's buy the commodity of X yuan a: 200 + (X-200) * 80% = 0.8x + 40 B: 100 + (X-100) * 90% = 0.9x + 10 when a = B: 0.8x + 40 = 0.9x + 10, then we can calculate x = 300 when a > b: x < 300 when a < B: x > 300, so when you spend 300 yuan, you can spend more than 300 yuan to go to a for shopping