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Now an entry into Fortnightly Topic Challenge #41: Short and Sweet

A man enters a room and presses a button. Within seconds he loses 20 lbs body weight. How did he lose the weight?

Yout Ried
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Quark-epoch
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19 Answers19

75

Since it's tagged 'lateral-thinking', an alternative that blatantly ignores the question's title is that:

The man is in the UK, and he just pressed 'OK' button to confirm a £20 purchase

Dave B
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    I thought of this first, but it specifies "weight" in the question, so this answer is invalid – Quintec Sep 24 '18 at 18:17
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    :jedi-hand-wave: Let's just call that a 'Financial Burden' then :P – Dave B Sep 24 '18 at 18:44
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    "Pounds" is abbreviated as "lbs.," which is never used for the currency. – Sneftel Sep 24 '18 at 19:34
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    However, did you know that the "£" symbol and the "lbs." abbreviation both have the same origin? They both essentially mean Libras (scales, used for measuring weight). – peaceoutside Sep 24 '18 at 20:30
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    Isn't this less "Lateral thinking" and more "Vertical thinking" ? – Selkie Sep 25 '18 at 16:56
  • Isn't the descent of the elevator the more vertical of the thought processes? :P – Dave B Sep 25 '18 at 17:03
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    @Quintec Because the Lift is faster than the Escalator, so he lost the wait. ;¬) – Chronocidal Sep 26 '18 at 08:09
  • OP should have used kilo instead. – Mixxiphoid Sep 26 '18 at 13:58
  • @Mixxiphoid - No, because you don't lose mass (kg) when the elevator begins its descent, only apparent weight - and using Newtons as a measure of weight would be an odd choice for the puzzle, too. – Dave B Sep 26 '18 at 14:04
  • @DaveB I don't get it, how would the question be any different if it was 10 kg, instead of 20lbs? They both represent mass, right? – Mixxiphoid Sep 26 '18 at 14:41
  • Excellent question! In our everyday lives, mass and weight seem like the same thing, but they're actually different. Mass is a measure of an object's inertia, or "how much energy does it take to accelerate this thing?". Weight is a measure of force, or "How hard does this thing push against that other thing?". When measuring these while standing still in Earth's gravity well, they're strongly related - the force exerted by you on whatever you're standing on is proportional to your mass (and the mass of the planet and how far away you are from its centre of mass) ... – Dave B Sep 26 '18 at 14:47
  • ... But if you are accelerating upwards or downwards (or if you go to a different planet), the force that you're exerting on whatever you're standing on will be different even though you are still made of the exact same mass - the number and type of atoms doesn't change. So when the elevator starts going down, the force you're exerting on the floor of the elevator is reduced slightly since the floor is 'falling' just a little bit with you. However, once the speed of the elevator becomes constant again, the forces are again balanced and the force you exert on the floor goes back to normal – Dave B Sep 26 '18 at 14:52
  • So to make a long response short, using kilograms instead of pounds would require that the person in the riddle actually loses mass - that is, to cause some significant number of atoms to disappear or no longer be considered part of their body. However, to lose weight we just need to reduce the force that is being exerted by the existing mass, and we can do that in much less traumatic ways. – Dave B Sep 26 '18 at 14:55
  • Hmm. Actually, reading the comments in the other answer, it sounds like I may have been under some misconceptions as well - when learning about the imperial system, I was always told that pounds was the base Imperial unit for weight - but apparently the term is ambiguous and there are different abbreviations that carry different meanings/connotations (!) ... That Imperial system is weird – Dave B Sep 26 '18 at 15:20
  • Eventually, using *kilo* as is could be interpreted both kilo*gram* (mass) or kilo*Newton* (force) - or kilo*anything* (1.000 anything) – Rafalon Sep 27 '18 at 07:27
  • Right, but the abbreviation kg (and not just k) would still be used, and that would unambiguously refers to only one of those. – Dave B Sep 27 '18 at 16:15
  • Also, I can't believe that this answer, which I cheekily acknowledge is a wrong answer in the first line, currently has more positive votes than the right one – Dave B Sep 27 '18 at 16:17
  • Nice try but see the question it is - How did he lose the WEIGHT? – Quark-epoch Sep 28 '18 at 09:50
  • @DaveB It's not wrong, from a certain point of view. – corsiKa Sep 30 '18 at 05:22
  • @Quark-epoch- I acknowledge that the answer is wrong multiple times and that this was just a cheeky response for a laugh. :) The 'WEIGHT' part is addressed (or at least hand-waved) in the first two comments. – Dave B Oct 01 '18 at 13:44
67

He entered

an elevator and pressed the down button. The downward acceleration from the elevator reduces his apparent weight.

Quintec
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    Doing the math for the average weight of 136lbs(62kg), acceleration of the elevator must be about -1.5 m/s^2. To put that in context, the average acceleration of an elevator is around -0.64 m/s^2. – David Starkey Sep 24 '18 at 20:42
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    lbs is mass, not weight... but blame it on the question. – vsz Sep 25 '18 at 06:10
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    @vsz: Nope. lbs is weight, not mass. You have it backward. "slugs" are the unit of mass in the Imperial system. – Beska Sep 25 '18 at 13:02
  • Does he add 20 lbf when the elevator goes up? Of course – DrD Sep 25 '18 at 16:12
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    The pound is a unit of both mass and force. The poundal is unambiguously a unit of force, which will give a mass of one pound an acceleration of one foot per second per second. The slug is unambiguously a unit of mass, which will be accelerated at one foot per second per second by a one pound force. – armb Sep 25 '18 at 16:32
  • https://en.wikipedia.org/wiki/Foot%E2%80%93pound%E2%80%93second_system#Variants – armb Sep 25 '18 at 16:37
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    @Beska : No, lbs, as currently legally defined, is mass. It's lbf which is force. – vsz Sep 25 '18 at 16:38
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    Are there any lifts/elevators that accelerate for several seconds? As soon as the lift ceases acceleration (which usually is sooner than "within seconds"), their normal weight is back... – Edheldil Sep 26 '18 at 16:13
  • Weight is a vector force, generally expressed as Newtons in a particular direction. Elevator acceleration varies by country. -1.5 m/s^2 is not unreasonable. Trap door water slides may give more. The room could also be a cockpit. – mckenzm Sep 27 '18 at 03:42
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    @vsz The legal definition would be relevant if this was a court of law. Usually weight means mass in legal contexts but force in engineering contexts (https://www.quora.com/Is-lb-a-unit-of-mass-or-force). The question mentions weight. It could be interpreted either way. – jbch Sep 27 '18 at 21:44
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    @DavidStarkey or the man is 306.4577012175 pounds. Perhaps he needs to lose some mass rather than weight. – user64742 Sep 30 '18 at 06:55
  • @Edheldil: As soon as the acceleration is reached, it counts as having happened “within seconds”. It’s okay if the pounds also come back within seconds. – Ry- Sep 30 '18 at 14:48
47

He presses the button to start a machine. It catastrophically fails within seconds and takes off the lower part of his leg, which weighed 20 lbs.

lPlant
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21

For an answer which exactly fits the question and the OP's clarifications...

He is wearing a diver's weight belt with a quick-release catch.

Graham
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18

He is:

Holding a 20 lbs of iron. The button activates a very powerful magnet.

Or:

In a room with some sort of anti-gravity (or, rather, gravity manipulating) feature. Just something that would slightly adjust the gravitational constant to make you lighter.

eye_am_groot
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16

A somewhat less morbid variant of an answer that's been posted a few times:

He has a prosthetic leg that weighs 20 pounds, and the button releases its clasp.

fluffy
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The man previously lost 20lbs and without knowing this he came to check his weight on a weight machine and pressed button to check his weight apparently in seconds the result popped up showing he lost 20lbs, looks very natural and correct answer ! dont ask me exactly how he lost 20 lbs :-)

Goose
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satyendra
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5

I know this already has a correct answer, but I'd like to offer an alternative:

The man works as a stocker and is holding 20lbs worth of cardboard. He enters the back room where he puts the cardboard in a baler and crushes it with the push of a button.

Joe-You-Know
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    According to my calculations, 20 lbs of cardboard is 152 square meters of cardboard, approximately a 12 by 12 meter piece of cardboard. No matter how you fold it, that'll be impossible to hold by one man. – Jacques Sep 27 '18 at 08:11
  • He loses 20 lbs BODY WEIGHT – Quark-epoch Sep 28 '18 at 09:49
5

It was an air lock of a submarine and filled the chamber with water, the buoyancy reduces his weight by 20 lbs.

or

The button published a new law that vital organs are owned by the government rather than the individual. He is no longer the legal owner of that weight.

or

The man was head of the International Committee for Weights and Measures and the button was publishing a new heavier definition of the pound.

PStag
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He walked into a Star Trek transporter (or similar) and transported himself to a planet where gravity was less strong.

Chris Bradshaw
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The button...

... triggers a guillotine which chops a leg off (apparently ~20lb for an adult male)

user52730
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A very

Lateral Thinking

type answer. You say that the man loses 20 lbs of body weight within seconds - but

you don't say how many seconds.

It could be

several billion seconds

or even just

7,776,000 seconds, which is three months.

Consequently, the button was

The doorbell in the lobby of his gym. (He goes to a very high-end gym.)

It's quite reasonable to lose 20 lbs of body weight

in three months of working out (and eating right). The first step was ringing the bell.

Community
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Brandon_J
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  • that is too lateral a thought to comprehend. This puzzle is too broad to be honest. I thought it would be closed for being too broad in the beginning but then it was unusually successful – Quark-epoch Sep 10 '19 at 15:48
  • @Quark-epoch I think it was close to being closed, but the answer you were looking for was fairly obvious IMO – Brandon_J Sep 10 '19 at 16:29
  • Yeah, I agree, I thought the same as this is such an absurd question. It was one of my first. – Quark-epoch Sep 11 '19 at 12:29
3

Upon pressing the button,

The entire room starts to accelerate downwards (for example, he is inside the lift) at an acceleration of a

So

Given that his original weight is Mg - Ma = 20lbs, we calculate the a given his mass M.

Kevin L
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Peter Teoh
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3

Simple, the man pressed

the buzzer on his door and let in a cleptomaniac bodybuilder who proceeded to steal his 20lb dumbbell. He lost his weight because he's too trusting of other people.

Suthek
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The man traveled to another planet where the gravity is less than his spacecraft. he opened the door of spacecraft and loss 20lbs of his weight. (assuming he created the room to adjust the gravity of that planet)

or

the man was using jetpack when he pressed the button he lost 20 lbs of his weight. ( he was trying to practice to use jetpack inside the big room of enough space and it can also be water jet)

or

man was a pilot when his plane takeoff he lost 20lbs of weight. ( he may enter the pilot room and press the take-off button and lose 20lbs weight )

or

man was carrying something attached to him with an electronic device when he pressed the button he lost 20lbs of weight because the luggage dropped.

Sayed Mohd Ali
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2

My first thought was:

He entered an elevator and pushed a button, causing the elevator to go down. The acceleration downwards is credited with making the man 20 pounds lighter, if only for a brief moment.

Then I thought of this:

If "lbs" stands for British pounds, then the man could have been at a gambling casino. He could have bet twenty pounds on red in a game of electronic roulette. When he pushed a button, the roulette ball landed on black, causing the man to lose his 20 pounds.

Thinking about it some more, I thought:

If the twenty pounds are truly weight, then the man could have simply been separated from something on his person. This could be an arm or a leg (separated by, oh, let's say a button-activated-spring-loaded-sawblade), or just something he was carrying. Maybe he was a delivery man delivering a 20 lb. package that was ordered on-line. He rings the doorbell, then within seconds a spring-loaded-saw... I mean, a grateful customer takes the 20 lb. package from the delivery man.

But then I thought some more, and I came up with:

Maybe he bought a collection of Richard Simmons' "Sweatin' to the Oldies" videos (I've seen some for around that price). I can't really explain how he'd lose so much weight "within seconds," unless I reinterpret "seconds" to mean "going back for seconds" (often heard when eating a meal). Maybe he liked the videos so much, he exercised a second time, or managed to lose enough weight despite having more portions of food.

J-L
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The button was connected to explosives hidden in this, this, this and seventeen more such buildings. When he presses the button, the twenty LBS are gone.

Robin
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He entered a vertical wind tunnel which got up to speed slowly as he stood there after pressing the button

xQbert
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-1

He enters lift, presses the button downwards. Psuedo acceleration upwards works here against gravity and weight measured is less now.

Let M be his mass and mg be weight before (outside lift)
Losing 20 lbs-
Pseudo acceleration is (Mg-20)/M unit length per square unit time

F1Krazy
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User12345
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    Exact same solution was already posted by Quintec. In addition please not to reveal spoilers by using >! at the beginning of a paragraph. – mpasko256 Sep 25 '18 at 10:05
  • I didn't see the response. Just the question. And I also gave the equations, so it's not the exact same. – User12345 Sep 25 '18 at 13:48