# Mysterious loss of weight

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?

• "Lateral Thinking" Oh! I get it!
– Vnge
Sep 24, 2018 at 18:07
• Nitpick: He loses 20 lbf. His mass stays the same.
– ohno
Sep 25, 2018 at 8:52
• He’s carrying 20 pounds of groceries in a bag, which he coincidentally drops on the floor a few seconds after pressing a completely unrelated button. Sep 25, 2018 at 13:58
• The pound is also a unit of currency. Sep 26, 2018 at 15:51
• This wasn't asked during the fortnightlly challenge- I don't think it's a valid submission. Nov 16, 2018 at 15:27

He entered

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

• 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. Sep 24, 2018 at 20:42
• lbs is mass, not weight... but blame it on the question.
– vsz
Sep 25, 2018 at 6:10
• @vsz: Nope. lbs is weight, not mass. You have it backward. "slugs" are the unit of mass in the Imperial system. Sep 25, 2018 at 13:02
• 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, 2018 at 16:32
• @Beska : No, lbs, as currently legally defined, is mass. It's lbf which is force.
– vsz
Sep 25, 2018 at 16:38

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

• I thought of this first, but it specifies "weight" in the question, so this answer is invalid Sep 24, 2018 at 18:17
• :jedi-hand-wave: Let's just call that a 'Financial Burden' then :P Sep 24, 2018 at 18:44
• "Pounds" is abbreviated as "lbs.," which is never used for the currency. Sep 24, 2018 at 19:34
• 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). Sep 24, 2018 at 20:30
• Isn't this less "Lateral thinking" and more "Vertical thinking" ? Sep 25, 2018 at 16:56

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.

• Should I be concerned this was my first thought too? Sep 24, 2018 at 17:35
• Somewhat along those lines would be someone in one of the Saw movies going to the next room and, well... lets just say traps and stuff. Sep 25, 2018 at 8:35
• It is a little too much deviation from the story Sep 28, 2018 at 9:49

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.

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.

• no he loses 20 lb body weight Sep 24, 2018 at 16:50
• Probably should specify that in the question :-) Sep 24, 2018 at 16:52
• well, rot13(va nagv-tenivgl ur jbhyq ybfr nyy uvf obql jrvtug abg whfg 20 yof naq 20 yof pna'g or uvf obql jrvtug) Sep 24, 2018 at 16:54
• what is he holding? Sep 24, 2018 at 16:55
• He had a metal leg? Sep 25, 2018 at 11:36

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.

• that is dammed clever. good one! Sep 26, 2018 at 20:24
• Why doesn't this answer have more upvotes? Sep 9, 2019 at 15:54

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 :-)

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.

• 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. Sep 27, 2018 at 8:11
• He loses 20 lbs BODY WEIGHT Sep 28, 2018 at 9:49

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.

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

The button...

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

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.

• 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 Sep 10, 2019 at 15:48
• @Quark-epoch I think it was close to being closed, but the answer you were looking for was fairly obvious IMO Sep 10, 2019 at 16:29
• Yeah, I agree, I thought the same as this is such an absurd question. It was one of my first. Sep 11, 2019 at 12:29

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.

• Nice answer, but next time you should really put your answers in spoilers :D Sep 26, 2018 at 2:22
• thank you Kevin. Sep 11, 2019 at 6:16

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.

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.

• Unfortunately, not the answer I was expecting but good try. +1 Sep 6, 2019 at 11:16

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.

• I like the thinking. The first part is already said but the second and fourth parts are intriguing Sep 28, 2018 at 9:46

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.

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

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

• Exact same solution was already posted by Quintec. In addition please not to reveal spoilers by using >! at the beginning of a paragraph. Sep 25, 2018 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. Sep 25, 2018 at 13:48