£11.80 and still none the wiser
Back in the day, the future Mrs BinDipper and I went to the cinema to see "Die Hard With a Vengeance". It was a mildly entertainment addition to the action genre that centered around John McClain trying to solve a number of riddles in Noo Yoik.

Now I don't think the missus and I would ever consider ourselves intellectuals, but neither would we think of ourselves as thick, so we were somewhat annoyed that we couldn't work out how one of the riddles had been solved.

The riddle was:

You have a three gallon water tank and a five gallon water tank. Place exactly four gallons of water on the scales to stop the bomb from exploding.

Writing it down now makes it looks like the simplest riddle ever, but at the time we were flummoxed to the point where we paid to see the film for a second time purely to see if we could 'get it'. We still couldn't work out what they'd done and it niggled at us for weeks. Bear in mind this was generally before you googled anything you couldn't understand.

I only worked it out when I watched it on the telly years later.
(BinDipper, Fri 14 Oct 2011, 10:52, 14 replies)

Aaaargh
I'm three beers in. What a horrible time to ask me this!
( difficultchild, Fri 14 Oct 2011, 11:07, closed)

Easy.
Just fill up the five-gallon tank to 4/5ths.

Jesus it's hardly brain science.
( Je suis un vagabond is an unfunny, up your own arse middle class knob, Fri 14 Oct 2011, 11:19, closed)

Alternatively
Fill the 3 gallon tank so that it's 1/3 full, empty into the 5 gallon tank, repeat a total of 4 times.

It's more lifting that way, mind.
(richardm, Fri 14 Oct 2011, 11:53, closed)

Ok...
So you empty the three gallon container, fill the five, then fill the three from the five so there's two left in the five, mark the spot on the five where the two comes to.
Empty the three out, pour the two gallons from the five back into it, then refill the five up to the mark you made earlier, add the two gallons you poured back into the three earlier and ta da! Four gallons.
Damn, that actually made my head hurt...
( difficultchild, Fri 14 Oct 2011, 11:21, closed)

Nah, you don't even need to leave a mark
You fill up the 3-gallon tank so there are 2 left in the 5-gallon tank, then empty the 2 gallons into the 3-gallon tank. Fill up the 5-gallon tank again and pour off 1 gallon into the space left in the 3-gallon tank. You've now got 4 gallons in the 5-gallon tank.

I was screaming at Bruce and Sam when they were doing this bit.
( emvee cruor deo cruoris, Fri 14 Oct 2011, 11:30, closed)

Also ...
Empty the 3 tank into the 5 tank twice, leaving you with 1 gallon left in the 3 tank. Empty the 5 tank, then stick the 1 gallon in it, plus a full 3 again.
( Wet-chinned bag shanker Cannot parse Wogan, Fri 14 Oct 2011, 11:37, closed)

Well yeah...
You could fill it to four fifths too I guess... like I said, drinking.
( difficultchild, Fri 14 Oct 2011, 11:22, closed)

easy
Fill the 3 gallon jug
Empty it into the 5 gallon jug
Fill the three gallon jug again
Fill the 5 gallon jug with the water in the three gallon jug leaving one gallon in the three gallon jug
Empty the 5 gallon jug
Pour the one gallon of water from the three gallon jug to the 5 gallon jug
Fill the three gallon jug and empty it into the 5 gallon jug
4 gallons
(andythepieman Is surfing the waves of indifference on, Fri 14 Oct 2011, 11:37, closed)

Mind piss ^

( Wet-chinned bag shanker Cannot parse Wogan, Fri 14 Oct 2011, 11:38, closed)

just ^^
Too thick to work it out for yourself then
(andythepieman Is surfing the waves of indifference on, Fri 14 Oct 2011, 16:50, closed)

I like the confusion, and convoluted solutions, this has generated.

( monster munch person, man, woman... camera... TV?, Fri 14 Oct 2011, 12:12, closed)

Does it have to be water?...

If you drain every drop of blood from 3 1/3* average people you will get 4 gallons?

I wonder why I'm never asked to solve problems at work?

*or 3 people and a dwarf I suppose.
( Pooflake braces for an onslaught..., Fri 14 Oct 2011, 13:04, closed)

What bugged me about that
...wasn't the puzzle so much, but if you watch it when Sam L Jackson is doing filling the buckets he sloshes loads of water out as he's doing it, so it would have been well less than 4 gallons by the time he'd finished.
( VicBrown I used to be narcoleptic but i'm alrig ,, Fri 14 Oct 2011, 15:44, closed)

American gallon
Imperial gallon has 10 lb of water,
American gallon has 8.
They didn't know which one to use for 4 gallons which is why the whole place gets blown to smithereens.
They jump up and dive down just as the shock wave passes over them so is doesn't really matter.
(the other guy not the one that gave you coochie warts, Tue 18 Oct 2011, 4:32, closed)