A man enters a room and presses a button. Within seconds he loses 20 lbs. How did he lose the weight?
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 :-)
It was an air lock of a submarine and filled the chamber with water, the buoyancy reduces his weight by 20 lbs.
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.
The man was head of the International Committee for Weights and Measures and the button was publishing a new heavier definition of the pound.
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.