There are a lot of interesting arithmetic problems hidden in life, let's just say this "20 yuan to buy soda" thing, 1 yuan 1 bottle, after drinking two empty bottles can also be exchanged for 1 bottle, at first glance it looks simple, carefully pondered and quite a doorway.

At the beginning, 20 yuan directly bought 20 bottles, and after drinking, I held 20 empty bottles in my hand.

Two empty bottles for 1 bottle, 20 empty bottles for 10 bottles, this will drink another 10 bottles, and the empty bottles become 10. Then change, 10 empty bottles for 5 bottles, and 5 empty bottles are left after drinking. At this time, don't worry, take 4 out of 5 empty bottles for 2 bottles, and after drinking, add the remaining 1 empty bottle, and there are 3 empty bottles. Take another 2 for 1 bottle, and after drinking the empty bottle, you can exchange it for 1 bottle.

In the end, after drinking this 1 bottle, there was 1 empty bottle in my hand, and I couldn't change it.

But it's even better to think about it another way: because "two empty bottles = one bottle of water (with bottle)", it can actually be split into "one empty bottle = one bottle of water (without bottles, just water)". After all, 1 yuan to buy 1 bottle (bottle of water), then the water is worth 0.

5 yuan, and 20 yuan can theoretically buy 40 servings of "water". But when you actually change it, there will be 1 empty bottle left in the end that can't be replaced, so you can drink 39 bottles at most.

It's the same as living in life, you have to be able to settle accounts and be flexible. Sometimes think about the problem from a different angle, it seems to be the top thing, and you can dig out some new doorways, just like this soda, counting, the number of bottles you drink is much more than at first glance, which is quite interesting! The next time you encounter something similar, you might as well pull it like this, maybe you can find a little surprise~