Wahaha, the price of each bottle of mineral water is 1.2 yuan. Now a and B stores offer preferential policies: 10% discount for all stores a, 20% discount for more than 20 bottles in B store, and no discount for less than 20 bottles in B store. If you are a consumer, which store is suitable? (consider four options)

Wahaha, the price of each bottle of mineral water is 1.2 yuan. Now a and B stores offer preferential policies: 10% discount for all stores a, 20% discount for more than 20 bottles in B store, and no discount for less than 20 bottles in B store. If you are a consumer, which store is suitable? (consider four options)

Examples of answers:
Suppose the consumer bought x bottles
The cost of shopping mall a = 0.9 × 1.2x
When x = 20, the cost is 20 × 1.2 + (x-20) × 0.8
First, when it's cost-effective,
1. When x=