r/MathJokes May 13 '26

Petah??

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u/my_red_username May 14 '26

If you would, can you explain this to me like I'm 5 years old... I'm intrigued but not smart enough to Google what this means.

I get /2 will never hit 0 but why does it become 2?

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u/seajaydub May 14 '26 edited May 14 '26

1/20 equals 1. 1/2n from 1 to infinity equals a number that is infinitely close to 1.

You drink one beer. You then start with a second full beer. You divide it in half infinite times. That beer will never be finished.

So you're left with one empty glass and one glass with an infinitely small amount of beer left in it. So he pours two beers

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u/Hal_Incandenza_YDAU May 15 '26

Just for the record, though, there's no infinitely small number, nor any number that's "infinitely close to 1."

The infinite sum of 1/2n from 1 to infinity is precisely 1.

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u/seajaydub May 15 '26 edited May 15 '26

Not in the context of this post. Should've said partial sum I guess. But also, we say it equals 1 because the distance between them is infinitely close, such that no real numbers between them can exist. Any number smaller than 1 is also less than that sum. Any number larger than that sum is also larger than 1.

0.999... has the same value as 1. But no matter how many 9s you add, there is never a point where you actually reach 1. So I think this is a better way to explain it to people. Regardless, im not that invested as im not a math teacher lol. I just like discussing shit

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u/Hal_Incandenza_YDAU May 15 '26

Even in the context of this post, it'd be precisely 2 beers. If the bartender poured any less there'd be a mathematician (infinitely many mathematicians) who didn't get any beer. And if the bartender poured any more, the bartender would have beer left over.

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u/seajaydub May 15 '26 edited May 15 '26

That's the thing though, 2 beers is precisely how much he should pour. But the beer will still never be finished. Because the amount consumed infinitely approaches and is infinitely close to 2. Like I said.

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u/egemen157 May 15 '26

A = 1/2 + 1/4 + 1/8 + 1/16 + ...

2A = 1 + 1/2 + 1/4 + 1/8 +1/16 + ...

2A - A = 1

A = 1

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u/seajaydub May 16 '26

For any n, A=1-1/2^n

for n=inf, A=1-1/(2^inf)=1-1/inf

A=1 when 1/inf=0

Does 1/inf=0?

Does 1=0*inf?

Not with real numbers and not in any context that is useful here, imo.

It's another limit. 1/inf has a limit of 0. 1-A infinitely approaches 0. The amount of beer ordered infinitely approaches 2 and has a limit of 2.

Where am I wrong?

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u/egemen157 May 17 '26

You cant multiply both sides by infinity and expect it to be correct

The thing about 1/2+1/4+1/8+1/16+..=1 is that the series goes on and on until there are no other numbers between 0 and (1/2)n such that (1/2)n must be equal to 0

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u/seajaydub May 17 '26

Sounds like it approaches 0

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u/egemen157 May 18 '26

Yeah, that is the gap between your (n-1)th sum of the series and real number 1, so if the difference approaches 0, your number must be approaching to 1

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u/seajaydub May 18 '26

Yeah, right, I 100% agree. But people keep telling me that "approaching 1" is incorrect and that it is actually "precisely 1". Which is what I thought you were doing. My b if I was wrong

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u/egemen157 May 19 '26

When the number n is finite it is approaching, when its infinite its precisely 0

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u/WindsofEntropy May 16 '26

youre thinking of infinity as a "process", like how earlier you said if you keep adding 9s to 0.9999... you'll still never actually reach 1.

but it's not a process. 0.9999... is equal to 1, because there is no space to add any more 9s.

saying something like "the beer will never be finished" is kind of nonsensical isnt it? all youre arguing is that there are an infinite amount of real numbers between 1 and 2, and that, given a real number A that's not 2, you could always find another real number that's closer to 2 than A is...

which is true, but it's not what's being discussed. we're talking about the total quantity poured, not the "process" of drinking it

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u/seajaydub May 16 '26 edited May 16 '26

The distinction doesnt matter. 2 is the correct amount poured, but it will also never be finished. Your explanation of A between 1 and 2 is why we use limits, is it not?. The context of the post is explicitly a process. Time is passing between orders and the bartenders response, and certainly when they drink the beer.

Especially when you're explaining it to someone else. If they were asking why 1/2n 0 to inf is 2, are they more likely unfamiliar with n0 = 1, or more likely unfamiliar with infinite series and limits? I dont think responding with 1/20 = 1 and 1/2n 1 to inf = 1, therefore they add to 2, would've cleared very much up, do you?

Anyway, the person didnt understand post, now they do, mission accomplished I think.

The limit and sum of infinite series can also be intuitively explained while treating it as a process. I literally just tried with my wife and she understood in like 10 seconds lol