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**regnar998****Member**- Registered: 2009-05-08
- Posts: 10

I've come across this weird little puzzle,

Infinity - Infinity = ???

Now when you first look at this you might think it equals zero. But look at it like this:

If you have infinity marbles and you give infinity (As in all of them) to someone else then infinity - infinity = nothing.

But if you have infinity marble numbered 1, 2, 3 etc. and gave every second marble to someone then infinity - infinity = infinity

BUT if you give someone else all the marbles numbered 3 or above (Which is infinity marbles) then infinity - infinity = 2.

But the question is in all these examples are you really giving infinity marbles away and do you still have infinity (Or whatever) left???

What do you guys think anyway?:)

Regnar

The 186,557,266-186,557,274 digits of PI is 12345678. (tinyurl.com/pisearch)

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 100,342

Hi regnar998;

Welcome to the forum. Look at this.

There is no single answer to this, as infinity is not a number in the strictest sense.

Infinity is a "limit". It is something you can get closer and closer to, but you never

quite reach it. What matters is how fast you approach the first infinity (call it

infinity01) versus how fast you approach the second infinity (call it infinity02). If

you approach both at exactly the same speed, always the same distance from each, then

infinity01-infinity02=0. If you are always a little closer to infinity01, then

infinity01-infinity02 is a positive number. If you move toward infinity01 twice as

fast as how you approach infinity02, then infinity01-infinity02=infinity. The behavior

of limits is not quite the same as the behavior of numbers.

Dr. Ken Mellendorf

I agree with some of this and some I am not sure of. Lets wait for some of the other posters who are way more rigorous to settle the question.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.** **Thinking is cheating.**

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**mathaholic****Member**- From: Earth
- Registered: 2012-11-29
- Posts: 3,051

Indeterminate!

Mathaholic | 17th most active poster | 771st most recent person to join MIFF | Person | rrr's classmate

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**Calligar****Member**- Registered: 2011-09-24
- Posts: 265

I would say undefined because infinity isn't a number. Infinity can be a difficult concept to understand when using it in ways such as that. I might suggest you look here to find out more about it...

There are always other variables. -[unknown]

But Nature flies from the infinite, for the infinite is unending or imperfect, and Nature ever seeks an end. -Aristotle

Everything makes sense, one only needs to figure out how. -[unknown]

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**mathaholic****Member**- From: Earth
- Registered: 2012-11-29
- Posts: 3,051

Calligar wrote:

He said undefined.

Mathaholic | 17th most active poster | 771st most recent person to join MIFF | Person | rrr's classmate

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**mathaholic****Member**- From: Earth
- Registered: 2012-11-29
- Posts: 3,051

julianthemath wrote:

I said indeterminate.

Indeterminate means you cannot tell the answer, because of infinity, meaning forever.

Mathaholic | 17th most active poster | 771st most recent person to join MIFF | Person | rrr's classmate

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