At the weekend, Xiao Gang and Chen Ming bought a bottle of soda after playing table tennis. Xiao Gang sucked soda with a straw, while Chen Ming thought that the straw was too thin and too slow to enjoy. He directly sucked soda with his mouth at the mouth of the bottle. Did Chen Gang's "quick" method work? Why?

At the weekend, Xiao Gang and Chen Ming bought a bottle of soda after playing table tennis. Xiao Gang sucked soda with a straw, while Chen Ming thought that the straw was too thin and too slow to enjoy. He directly sucked soda with his mouth at the mouth of the bottle. Did Chen Gang's "quick" method work? Why?

A: it doesn't work. Because when we suck on one end of the straw with our mouth, the other end of the straw is in the soda water. When we empty the air in the straw, this end is equivalent to a vacuum. At this time, the atmospheric pressure in the air makes the soda water enter our mouth through the other end of the straw. After sealing the soda bottle with our mouth, the external atmospheric pressure can't act on the top of the soda water, but can't press the soda water up ．

A school held a sports meeting and planned to give each of 1991 students a bottle of soda. Because the store stipulated that every seven empty bottles could be replaced with one bottle of soda, so it was not necessary to buy 1991 bottles of soda. How many bottles of soda should I buy at least?
Use arithmetic instead of equations

1991÷8=248——7
248×7+7=1743

The school sports meeting plans to give 1000 students each a bottle of soda. Because the store stipulates that every five empty bottles can be exchanged for one bottle of soda, so
You don't have to buy 1000 bottles of soda. How many bottles at least?
It seems to use the set value method
Set: 1 yuan for an empty bottle, 4 yuan for a soda, 5 yuan for a soda

1000 (5 + 1) = 166 bottles. 41000-166 = 834 bottles
A: you can buy 834 bottles less

A school held a sports meeting and planned to give each of the 1995 students a bottle of soda. Because the store stipulates that every six empty bottles can be exchanged for one bottle of soda, it is not necessary to buy 1995 bottles of soda, but at least how many bottles?

Because the store stipulates that every six empty bottles can be exchanged for a bottle of soda: Meaning: buy six bottles of soda can be exchanged for one more bottle, enough for seven people to drink, you can take these seven people as a group, 1995 divided by 7, equal to 285 groups, each group only needs six bottles, namely: 285 * 6 = 1710 bottles, the formula is "1995 / (6 + 1) * 6 = 1710, I this is a general algorithm, for such problems