### Roland DürreFriday November 16th, 2018

## Unbelievable but Likely .

I read the following dialogue as reported and commented in a tweet. I want to hand it on to you with my own comments:

Two teenagers in a bus:

*“If you take the year 2018 and subtract your age, you will get the year of your birth!” *

”Wow, it’s true! Great!“

We are lost. All of us

And I must admit that I immediately did my own mental calculations. And the result was truly stunning:

Yes, it is correct!

2018 – 68 = 1950

I even did the reverse mathematics as a test:

1950 + 68 = 2018

Also true!

And then I felt truly embarrassed.

? After all, the difference between the year you have and the year of your birth is defined as your age, isn’t it? Consequently, it has to work.

But what would happen if, on a huge stage, I would say that the year 2018 is a very special year because, exactly as the year ends (on December, 31st), the sum of their year of birth and their current age in years would be 2018 for all living people? And if I would add the comment that this is really something special?

I guess that most of the audience would quickly do their own calculations to find out if it is true for them and then accept this truly asinine statement of mine. And that only very few would get up and leave the lecture hall because the speaker is telling such rubbish. Because people are used to believing what they are told. And asking critical questions is no longer fashionable.

Incidentally, this is where we touch the origins of mathematics. The age of a person is a good example for the axiom of the natural numbers {0,1,2 … n, n+1} (except that the natural numbers are, by definition, infinite – which is only true for the number of years a person has lived if there is eternal life). To be sure, you can still have an argument about whether or not zero is a natural number. I would say this is a pure matter of definition.

You can perform the operation “add“ on the natural numbers – the same is true for the operation “multiply“ that is derived from the adding operation – and yet you will remain in the domain “natural numbers “.

Our measuring of time with the arbitrarily fixed point zero that is supposed to have been the time Christ was born can be an example for the ”Whole Numbers“– as we all know, they are constructed from the natural numbers through another operation, the subtraction. Just like you can construct the rational numbers from the whole numbers through the operation of division.

These are the kinds of ideas I had after my first shock had subsided. And now I am even more surprised to see that some people are actually surprised about getting a as a result of a subtraction of b and c.

(**c** – **b** = **a**) and similarly of c being the result of an addition of **a** and **b** (**a** + **b** = **c**).

**a** = year of birth **b** = age **c** = current year

Wow. Extraordinary?

RMD

(Translated by EG)

### 1 Kommentar zu “Unbelievable but Likely .”

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KH(Saturday November 17th, 2018)Echt krass Roland! Aber jetzt will ich diese tiefe Erkenntnis doch auch mathematisch sauber fassen: da gilt nämlich

2018 – Alter = 2018 – (2018 – Geburtsjahr) = Geburtsjahr

d.h. in meinem Fall in Zahlen,

2018 – (2018 – 1941) = 1941 !!!

Klug die Jungs, echt! Ich kenne nämlich jetzt mein Geburtsjahr ohne mein Alter preis gegeben zu haben!Toll!

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