Fill the 3 gallon jug, empty it into the five gallon jug. Now you have 3 gallons of water in the 5 gallon jug.
Fill up the 3 gallon jug again. Now pour 2 gallons of it into the 5 gallon jug which already has 3 gallons of water in it from before. The 5 gallon jug is now full and the 3 gallon jug has 1 gallon of water remaining in it.
Then dump the 5 gallon jug out and pour the 1 gallon of water in from the 3 gallon jug. That makes 1 gallon of water in the 5 gallon jug.
Refill the 3 gallon jug now and then pour it into the 5 gallon jug which has 1 gallon of water already in it for a grand total of 4 gallons of water in the 5 gallon jug.

In that case the bad guy would have given them a harder riddle, one that couldn't be solved through googling. Or even easier, the bad guy had them in his control, he could have easily asked them to just drop any smartphone.

In today's world of smartphones they would have just Googled all the answers of the riddles.
I am a very decisive person, I think.

No, you were right the first time, the bomb that required to solve the riddle with the gallon containers had a proximity circuit too.

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OH, I guess I didn't catch that part. Thanks. I wonder if I can remember the answer now! It is still a little confusing even after reading the solution!

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Personally, I would have run across the street to buy a gallon container of anything.

This scene is so stupid, it totally halts the film, and i've seen it give trouble to many a viewer ever since it was released. Hey everybody, lets go to school! Weeee.
"I said no camels, that's five camels, can't you count?"

Must admit, I didn't get it until my third viewing.

They "explain" it in the film.
And so, God came forth and proclaimed widescreen is the best.
Sony 16:9

what they should have done considering thw water they had, was fill them both half full.. that would be 2 1/2 gallons in the 5 gallon jug, and 1 1/2 in the 3 gallon jug, and then combine them. 2 1/2 + 1 1/2 =4. boom, they had their solution!!!
More like boom, there goes the entire block after the bomb goes off. They had to get
precisely
four gallons of water, no margin for error.
'Remember when' is the lowest form of conversation.

Tony Soprano

It had to be precise to the ounce though, so that wouldn't have worked.

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what they should have done considering thw water they had, was fill them both half full.. that would be 2 1/2 gallons in the 5 gallon jug, and 1 1/2 in the 3 gallon jug, and then combine them. 2 1/2 + 1 1/2 =4. boom, they had their solution!!!

@wears lololol that's funny how you are trying to defend your mistake by arrogantly making out you were merely answering the question of the riddle, in your opinion the 'easier' way, when your way takes longer, I count 8 steps in total, than the correct and actual easier way that they do in the movie which is 6 steps. So nah, you fail!

Yeah, I explained tge shorter (in my opinion easier) way to do it. The OP was asking the solution to the riddle, but as you say that wasn't how they did it in the movie

I remember they have 2 gallons left in the 3 gallons.
That's mean, they (McClaine and Zeus, most probably off screen):-
Fill 5 gallons bottle full
Pour 3 gallons into 3 gallons bottle (5 gallons bottle have 2 gallons left)
Empty the 3 gallons bottle
Transfer the 2 gallons remaining in 5 gallons bottle to 3 gallons bottle
That's how they have 2 gallons in a 3 gallons bottle.
What they do is:-
Fill 5 gallons bottle full again
Pour 1 gallons into 3 gallons bottle
So the 5 gallons bottle will have 4 gallons.
Yours are not wrong, just not the way they did it.

Yes.
Fill the 3 gallon bottle and empty it into the 5 gallon. Fill it again and empty into 5 gallon until full. This leaves 1 gallon in the 3 gallon bottle. Empty all the water from the 5 gallon and pour the remaining 1 gallon from the 3 gallon into the 5 gallon. Refill the 3 gallon and pour it into the 5 gallon.
Exactly 4 gallons!!!
Gentlemen, England will be playing 4-4-fing-2