# Isn't it obvious?

#### Yaakov

Joined Jan 27, 2019
3,153
One exceptionally pleasant day a mathematician, a physicist and a biologist decided to lunch at a nearby sidewalk café. As they sat eating, they observed the people coming and going around them. They watched as across the street one person, then another entered a building. A few minutes later, the two original people left in the company of a third.

"Did you see that?" said the biologist, "They reproduced!."
"Don't be silly.", said the physicist, "There was clearly a measurement error."
"You are both very funny.", said the mathematician, "It's obvious that if exactly one more person enters that building it will be empty."

#### DickCappels

Joined Aug 21, 2008
7,426
Ho ho! One of my favorites!

#### bogosort

Joined Sep 24, 2011
674
"It's obvious that if exactly one more person enters that building it will be empty."
I don't get it; can you add a spoiler tag with an explanation?

#### Papabravo

Joined Feb 24, 2006
16,107
I don't get it; can you add a spoiler tag with an explanation?
If you assume the initial contends of the building is zero, two people enter and three people leave, the number of people in the building is now -1. This is only possible in the abstract world of Mathematics.

#### bogosort

Joined Sep 24, 2011
674
If you assume the initial contends of the building is zero, two people enter and three people leave, the number of people in the building is now -1. This is only possible in the abstract world of Mathematics.
Ah, thank you for the explanation. I'm disappointed with the joke as it never occurred to me to assume that the building was initially empty.

#### crutschow

Joined Mar 14, 2008
27,190
Here's my favorite engineering joke, if you haven't seen it.

#### cmartinez

Joined Jan 17, 2007
7,332
This is the sort of joke that makes you laugh three times: when you first read it, when it's explained to you, and when you finally get it...

#### killivolt

Joined Jan 10, 2010
800
If you assume the initial contends of the building is zero, two people enter and three people leave, the number of people in the building is now -1. This is only possible in the abstract world of Mathematics.
I thought it was zero base numbering, therefor we have 2 people leave in the company of a third. Still leaving -1, third person forgot his keys went back in as the door locks behind him, now zero again, poor bugger he has to wait for someone to open the door again

kv

#### cmartinez

Joined Jan 17, 2007
7,332
I thought it was zero base numbering, therefor we have 2 people leave in the company of a third. Still leaving -1, third person forgot his keys went back in as the door locks behind him, now zero again, poor bugger he has to wait for someone to open the door again

kv
Which begs the question... how were the aforementioned building's stories numbered? ... was the floor immediately above ground assigned the number one, or number two?

#### djsfantasi

Joined Apr 11, 2010
7,689
Ah, thank you for the explanation. I'm disappointed with the joke as it never occurred to me to assume that the building was initially empty.
Ah, but mathematically, it’s the only assumption that makes sense. How appropriate!

#### Papabravo

Joined Feb 24, 2006
16,107
Which begs the question... how were the aforementioned building's stories numbered? ... was the floor immediately above ground assigned the number one, or number two?
At one particular hotel in Las Vegas the floor above the Lobby is #14. It is true that the lobby has a high ceiling.

#### cmartinez

Joined Jan 17, 2007
7,332
At one particular hotel in Las Vegas the floor above the Lobby is #14. It is true that the lobby has a high ceiling.
Lucky for everyone... floor numbering didn't start at #13 ...

#### Papabravo

Joined Feb 24, 2006
16,107
You're right it may have been intentional in a gambling mecca as a way to sidestep the unluckiest of numbers. It is curious that it is on the wheel (roulette) however,

#### cmartinez

Joined Jan 17, 2007
7,332
If memory serves me right, there are a few buildings in the world that deliberately skip the 13th floor.

Sometimes there's a gap in the structure itself, and sometimes said number is conspicuously absent with no apparent architectural cause.

#### Alec_t

Joined Sep 17, 2013
12,065
Sometimes there's a gap in the structure itself
So levitation is relied on to support floor 14 and above?

#### atferrari

Joined Jan 6, 2004
4,322
So levitation is relied on to support floor 14 and above?
No. Look for the chains.

And sorry, stairs not available yet.