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3 + 5 = 4

 3 + 5 = 4
type
FeatureClass
 3 + 5 = 4
label
3 + 5 = 4
 3 + 5 = 4
page
ThreePlusFiveMakeFour
 3 + 5 = 4
comment
You have two containers, one that holds 3 liters and one that holds 5 liters, and access to a water source. Place exactly 4 liters of water into either a third container (one that holds at least 5 liters, so that you can't simply fill the container to the brim and be done with it) or the 5-liter container (depending on the version).
This puzzle dates back at least as far as the 1920s, and quite possibly earlier still. Some versions replace the jugs with sand timers for cooking eggs and the liters with minutes.
One solution is as follows:
Fill the 5-liter container.
Fill the 3-liter container from the 5-liter container, leaving 2 liters.
Empty the 3-liter container. Then, pour the remaining 2 liters from the 5- to the 3-liter container.
Refill the 5-liter, then fill the 3-liter from the 5-liter container. You will be left with 4 liters in the 5-liter container.
Another alternate solution, though this one requires several assumptions: The containers must have at least one line of symmetry when looking at them from the top, and they must have a constant width. (Cylinders or rectangular prisms meet this requirement.)
Fill the 5-liter container, then place one part of the bottom down, and tilt it until the water level makes a straight line from the upper edge of the bottom to the bottom edge of the lip.
Do the same thing with the 3-liter container, and pour it into the 5-liter container.
2.5 + 1.5 = 4
It bears noting that this puzzle, like many other stock puzzles, is usually difficult only because the solver is overthinking it. In practice, if you actually have the two jugs, and you just start filling one jug and pouring it into the other, the solution presents itself very quickly. (This is incorporated in some tellings of the riddle, which demand that you come up with the answer in less than a minute, as An Aesop about the value of trying things out rather than just sitting there thinking.)
Maths nerd bit: You're looking for the smallest integer x and y that satisfy 3x−5y=4; then fill the 3-liter x times, pouring it into the 5-liter when full, and emptying the 5-liter when it's full (which you'll do y times). The solution is x=3 and y=1. The solution up there is the dual formulation, 5x−3y=4 (x=2, y=2). From here, two details present themselves: one, that it's easily adaptable to values other than 3 and 5, and two, that a solution exists only if the target value is a multiple of the highest common factor of the container sizes (e.g. you can't get 4 liters from 6- and 3-liter containers).
Not necessarily related to Solve the Soup Cans.
Nothing to do with 2 + Torture = 5.
 3 + 5 = 4
fetched
2023-11-04T19:14:45Z
 3 + 5 = 4
parsed
2023-11-04T19:14:45Z
 3 + 5 = 4
isPartOf
DBTropes
 3 + 5 = 4 / int_219a8958
type
3 + 5 = 4
 3 + 5 = 4 / int_219a8958
comment
Myst IV: Revelation has a slight variation of this by rerouting Tomahna's backup power from two locations on the Age, to the two gates on its hydroelectric dam.
 3 + 5 = 4 / int_219a8958
featureApplicability
1.0
 3 + 5 = 4 / int_219a8958
featureConfidence
1.0
 Myst IV: Revelation (Video Game)
hasFeature
3 + 5 = 4 / int_219a8958
 3 + 5 = 4 / int_27faf621
type
3 + 5 = 4
 3 + 5 = 4 / int_27faf621
comment
In one episode of Cyberchase, the kids and Digit have to input exactly one cup of sand into a device to open a castle gate. Digit has a 2-cup and 3-cup measure, but is missing his 1-cup measure. At first they try filling the 2-cup halfway, but are unable to get it precise enough. Then they figure out they can fill the 3-cup measure, pour enough sand from it to fill the 2-cup, and be left with exactly one cup.
 3 + 5 = 4 / int_27faf621
featureApplicability
1.0
 3 + 5 = 4 / int_27faf621
featureConfidence
1.0
 Cyberchase
hasFeature
3 + 5 = 4 / int_27faf621
 3 + 5 = 4 / int_30445b95
type
3 + 5 = 4
 3 + 5 = 4 / int_30445b95
comment
The Castle of Dr. Brain has a form of this with its hourglass puzzle. Measure 40 seconds by flipping 2 hourglasses that last 35 and 15 seconds (or 25 and 15 on easy difficulty).
 3 + 5 = 4 / int_30445b95
featureApplicability
1.0
 3 + 5 = 4 / int_30445b95
featureConfidence
1.0
 Dr. Brain (Video Game)
hasFeature
3 + 5 = 4 / int_30445b95
 3 + 5 = 4 / int_4cd59767
type
3 + 5 = 4
 3 + 5 = 4 / int_4cd59767
comment
In Fermat's Room, there's a variant with two hourglasses: one of four minutes and one of seven minutes, and the goal is to time nine minutes. Answer is to start both hourglasses at once (t=0), turn the four-minute one over once it runs out (t=4), then once the seven-minute one runs out (t=7) start counting — there's one minute of sand left in the smaller one at that point, then just flip it two more times to get the other eight minutes needed.
 3 + 5 = 4 / int_4cd59767
featureApplicability
1.0
 3 + 5 = 4 / int_4cd59767
featureConfidence
1.0
 Fermat's Room
hasFeature
3 + 5 = 4 / int_4cd59767
 3 + 5 = 4 / int_526d4c5c
type
3 + 5 = 4
 3 + 5 = 4 / int_526d4c5c
comment
In Knights of the Old Republic on Manaan, this puzzle appears in the form of pressurized canisters that control the Kolto harvester, where you must transfer the fuel for the machinery back and forth until you have four units in the large tank which will destroy the machine. Solving it is a prerequisite for the "good" ending on that planet.
 3 + 5 = 4 / int_526d4c5c
featureApplicability
1.0
 3 + 5 = 4 / int_526d4c5c
featureConfidence
1.0
 Knights of the Old Republic (Video Game)
hasFeature
3 + 5 = 4 / int_526d4c5c
 3 + 5 = 4 / int_6860eda7
type
3 + 5 = 4
 3 + 5 = 4 / int_6860eda7
comment
In the 2006 spiritual successor of Safe Cracker, this must be done to turn on the fountain in Duncan W. Adams' mansion, by rerouting water between three pistons.
 3 + 5 = 4 / int_6860eda7
featureApplicability
1.0
 3 + 5 = 4 / int_6860eda7
featureConfidence
1.0
 Safe Cracker / Videogame
hasFeature
3 + 5 = 4 / int_6860eda7
 3 + 5 = 4 / int_7870fd09
type
3 + 5 = 4
 3 + 5 = 4 / int_7870fd09
comment
In Zork Zero, one puzzle involves obtaining 6 "gloops" of water using a 9-gloop vial and a 4-gloop vial. Obtaining the 4-gloop vial is a multi-stage puzzle in itself.
 3 + 5 = 4 / int_7870fd09
featureApplicability
1.0
 3 + 5 = 4 / int_7870fd09
featureConfidence
1.0
 Zork Zero (Video Game)
hasFeature
3 + 5 = 4 / int_7870fd09
 3 + 5 = 4 / int_84986bf9
type
3 + 5 = 4
 3 + 5 = 4 / int_84986bf9
comment
Appears in RuneScape, among other Stock Puzzles: During the Fremennik Trials, among the series of tasks to get a Frozen Key in Peer the Seer's portion is measuring 4 units of water from a 5-unit bucket and 3-unit jug and then pouring that amount of water into a vase.
 3 + 5 = 4 / int_84986bf9
featureApplicability
1.0
 3 + 5 = 4 / int_84986bf9
featureConfidence
1.0
 RuneScape (Video Game)
hasFeature
3 + 5 = 4 / int_84986bf9
 3 + 5 = 4 / int_8694f6ad
type
3 + 5 = 4
 3 + 5 = 4 / int_8694f6ad
comment
A variation of this puzzle occurs in Fatal Hearts, where you need ⅔ cup of flour but have only an 800ml cup and a 100ml cup. The puzzle's not too hard if you're good at conversions.
 3 + 5 = 4 / int_8694f6ad
featureApplicability
1.0
 3 + 5 = 4 / int_8694f6ad
featureConfidence
1.0
 Fatal Hearts (Visual Novel)
hasFeature
3 + 5 = 4 / int_8694f6ad
 3 + 5 = 4 / int_892aa56a
type
3 + 5 = 4
 3 + 5 = 4 / int_892aa56a
comment
In the Murdoch Mysteries episode "Breaking Ranks", a subplot has Julia giving the constables an IQ test devised by a friend of hers. The first question is a variant of the puzzle. Higgins misses the point:
 3 + 5 = 4 / int_892aa56a
featureApplicability
1.0
 3 + 5 = 4 / int_892aa56a
featureConfidence
1.0
 Murdoch Mysteries
hasFeature
3 + 5 = 4 / int_892aa56a
 3 + 5 = 4 / int_8d87d97a
type
3 + 5 = 4
 3 + 5 = 4 / int_8d87d97a
comment
In an episode of Zoom, Jessie and Zoe are challenged to divide 10 quarts of water into two equal parts using only a 10-quart bucket, a 7-quart bucket, and a 3-quart pitcher, leaving 5 quarts each in the two buckets and the pitcher empty (5/5/0). To start, all 10 quarts are in the larger bucket (10/0/0). When transferring water from one container to another, they must fill that container all the way, or use the entire remaining volume of the container they're pouring from, whichever comes first. Zoe keeps track of the three volumes on an easel. After at least 20 transfers (with Zoe's chart now on a second page), they eventually get to 1/7/2. It is at this point that Jessie figures out how to reach the goal of 5/5/0: transfer the 7 quarts to the 10-quart bucket (8/0/2), then the 2 quarts into the empty 7-quart bucket (8/2/0), then use the 8 quarts to fill the empty 3-quart pitcher (5/2/3), and finally, pour the 3 quarts into the 7-quart bucket, adding to the 2 quarts already in there.
 3 + 5 = 4 / int_8d87d97a
featureApplicability
1.0
 3 + 5 = 4 / int_8d87d97a
featureConfidence
1.0
 Zoom
hasFeature
3 + 5 = 4 / int_8d87d97a
 3 + 5 = 4 / int_9fe76e58
type
3 + 5 = 4
 3 + 5 = 4 / int_9fe76e58
comment
The final level of Tomb Raider: The Last Revelation contains a portion with two instances of the puzzle. In the first, Lara uses two waterskins, a 5-liter and a 3-liter, to pour 2 liters of water into a pitcher on a scale, opening a grate in the floor. In the second, she uses the same two waterskins to pour 4 liters of water, opening another grate.
 3 + 5 = 4 / int_9fe76e58
featureApplicability
1.0
 3 + 5 = 4 / int_9fe76e58
featureConfidence
1.0
 Tomb Raider: The Last Revelation (Video Game)
hasFeature
3 + 5 = 4 / int_9fe76e58
 3 + 5 = 4 / int_a7ba84d2
type
3 + 5 = 4
 3 + 5 = 4 / int_a7ba84d2
comment
In Phantasmat, this puzzle appears in a chapter where you must switch on a generator. Part of the tasks involves putting a jug of 4 units of liquid on a weight, and you only have a 5-unit bottle and 3-unit bottle to get 4 units.
 3 + 5 = 4 / int_a7ba84d2
featureApplicability
1.0
 3 + 5 = 4 / int_a7ba84d2
featureConfidence
1.0
 Phantasmat (Video Game)
hasFeature
3 + 5 = 4 / int_a7ba84d2
 3 + 5 = 4 / int_abd7c3a3
type
3 + 5 = 4
 3 + 5 = 4 / int_abd7c3a3
comment
Club Penguin: EPF mission 10, Waddle Squad, has Jet Pack Guy running out of fuel for his jet pack. He can make some emergency fuel with cream soda, and two containers of 4 are needed. You have to distribute the cream soda between glass containers of 8, 5, and 3.
 3 + 5 = 4 / int_abd7c3a3
featureApplicability
1.0
 3 + 5 = 4 / int_abd7c3a3
featureConfidence
1.0
 Club Penguin (Video Game)
hasFeature
3 + 5 = 4 / int_abd7c3a3
 3 + 5 = 4 / int_c897a969
type
3 + 5 = 4
 3 + 5 = 4 / int_c897a969
comment
Rusty Lake Hotel has a puzzle like this, in order to pour a certain amount of water into a flask, for use in a distiller nearby.
 3 + 5 = 4 / int_c897a969
featureApplicability
1.0
 3 + 5 = 4 / int_c897a969
featureConfidence
1.0
 Cube Escape (Video Game)
hasFeature
3 + 5 = 4 / int_c897a969
 3 + 5 = 4 / int_c9cd78c2
type
3 + 5 = 4
 3 + 5 = 4 / int_c9cd78c2
comment
In the movie Die Hard with a Vengeance, the two main characters must solve this type of puzzle in order to disarm a bomb near a public fountain. In the original script, the bomb was a Chekhov's Gun, as the movie would end with McClane planting the bomb on the bad guy's helicopter, and upon discovery one of them asks if anyone has a four gallon jug (in the final script the bomb was used for something else entirely without the puzzle being brought up again).
 3 + 5 = 4 / int_c9cd78c2
featureApplicability
1.0
 3 + 5 = 4 / int_c9cd78c2
featureConfidence
1.0
 Die Hard with a Vengeance
hasFeature
3 + 5 = 4 / int_c9cd78c2
 3 + 5 = 4 / int_cb1d762a
type
3 + 5 = 4
 3 + 5 = 4 / int_cb1d762a
comment
Poptropica: On Wimpy Wonderland Island, you have to distribute some wiper fluid between a 10 liter bottle, 5 liter cup, and 3 liter dog dish. You need to move the wiper fluid around until you end up with 4 liters.
 3 + 5 = 4 / int_cb1d762a
featureApplicability
1.0
 3 + 5 = 4 / int_cb1d762a
featureConfidence
1.0
 Poptropica (Video Game)
hasFeature
3 + 5 = 4 / int_cb1d762a
 3 + 5 = 4 / int_f682e7ae
type
3 + 5 = 4
 3 + 5 = 4 / int_f682e7ae
comment
A more complex version of this classic puzzle appears at the end of Sherlock Holmes Versus Arsène Lupin, where you have to measure exactly 478cc of black powder with only 250cc, 80cc and 12cc containers at your disposal. While pouring powder back and forth is an option (1x250 + 3x80 − 1x12=478), there are other ways to solve the puzzle, such as: 1x250 + 19x12=478.
 3 + 5 = 4 / int_f682e7ae
featureApplicability
1.0
 3 + 5 = 4 / int_f682e7ae
featureConfidence
1.0
 Sherlock Holmes Versus Arsène Lupin (Video Game)
hasFeature
3 + 5 = 4 / int_f682e7ae
 3 + 5 = 4 / int_f6bb880b
type
3 + 5 = 4
 3 + 5 = 4 / int_f6bb880b
comment
This puzzle and several variants appear in the Professor Layton series. The Curious Village has three variations: "Juice Pitcher", which is as described above but involving a full 8-quart/litre pitcher of tomato(?) juice; "Milk Pitchers", where you have to use a 7- and 3-quart/litre pitchers to distribute 10 litres of milk in two parts of 5; and "Water Pitchers", which asks you to divide a 16- and 9-quart/litre pitchers until they each hold 8 quarts/litres of water.
 3 + 5 = 4 / int_f6bb880b
featureApplicability
1.0
 3 + 5 = 4 / int_f6bb880b
featureConfidence
1.0
 Professor Layton (Video Game)
hasFeature
3 + 5 = 4 / int_f6bb880b

The following is a list of statements referring to the current page from other pages.

 3 + 5 = 4
processingCategory2
Stock Puzzle
 Die Hard with a Vengeance / int_98ed60b9
type
3 + 5 = 4
 Fermat's Room / int_98ed60b9
type
3 + 5 = 4
 Perplex City (Tabletop Game) / int_98ed60b9
type
3 + 5 = 4
 Dr. Brain (Video Game) / int_98ed60b9
type
3 + 5 = 4
 Knights of the Old Republic (Video Game) / int_98ed60b9
type
3 + 5 = 4
 Professor Layton (Video Game) / int_98ed60b9
type
3 + 5 = 4
 The Trader of Stories (Video Game) / int_98ed60b9
type
3 + 5 = 4
 Tomb Raider: The Last Revelation (Video Game) / int_98ed60b9
type
3 + 5 = 4
 Zork Zero (Video Game) / int_98ed60b9
type
3 + 5 = 4
 Cyberchase / int_98ed60b9
type
3 + 5 = 4