Class 6 (2) is going to have a spring outing. The price of a brand of milk is 2 yuan per bottle. If you buy it in department store a, you can get a free bottle of 5 bottles; if you buy it in department store B, you can get 10% discount. There are 42 students in the class. If you want to prepare a bottle of such milk for each student, which department store should you go to

Class 6 (2) is going to have a spring outing. The price of a brand of milk is 2 yuan per bottle. If you buy it in department store a, you can get a free bottle of 5 bottles; if you buy it in department store B, you can get 10% discount. There are 42 students in the class. If you want to prepare a bottle of such milk for each student, which department store should you go to

5 × 7 + 7 = 42, 35 × 2 = 70 (yuan), 42 × 2 × 0.9 = 75.6 (yuan)

A brand of milk 200 ml per box, the price of 2 yuan. In a shop to buy, buy 5 boxes to get 1 box; in B shop to buy, 10% discount. 42 people in the class, to each
One of the students prepared a box of such milk. Which shop should I go to to buy it? Why?

It only costs 70 yuan for store a and 75.6 yuan for store B. which one do you want to go to?

1 yuan for a bottle of mineral water, after drinking two empty bottles can change a bottle of soda, ask: you have 20 yuan, can drink a few bottles of mineral water at most? Why?

39 bottles, because: 20 yuan to buy 20 bottles, there are 20 empty bottles, change 10 bottles of water, there are 10 empty bottles, change 5 bottles of water, there are 5 empty bottles, change 2 bottles of water, the remaining one bottle, 2 bottles of water for 1 bottle, this bottle plus the rest for 1 bottle, a total of 20 + 10 + 5 + 2 + 1 + 1 = 39

Star Supermarket mineral water 1.5 yuan a bottle, buy 10 bottles of 20% discount. Lili bought mineral water spent 18 yuan, she bought a total of how many bottles of mineral water?

18 ÷ (1.5 * 80%) = 15 bottles
This is the first answer. I wish you progress!