# A riddle

You have got two buckets of capacity 3 litres and 5 litres each and a tap. How will you exactly measure out 4 litres of water with the help of two buckets and the tap.

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You fill up 5 liter one from the tap. Then fill up 3 liter one from 5 liter one. Then empty the 3 liter one. Then split what's left in 5 liter in two buckets. Then fill up the 3 liter one again and pour it into the 5 liter one.

jedishrfu
Mentor
1) fill the 5 liter and pour into the 3 liter until full leaving 2 liter in the 5 liter bucket.

2) empty the 3 lt bucket and pour the remaining 2 lt from the 5 lt bucket into the 3lt.

So the 3 liter bucket now has 2 liters in it.

3) Lastly fill the 5 liter completely and then pour it into the 3liter bucket until the 3 liter bucket is full.

Since the 3 liter bucket had 2 liters in it then you've out 1 liter so that what remains in the 5 liter bucket is 4 liters.

davenn
Danger
Gold Member
I'd calculate the height of 4 litres in the confines of the 5 litre bucket, then draw a line at that point and fill to there using the 3 litre bucket as a source.

jedishrfu
Mentor
I'd calculate the height of 4 litres in the confines of the 5 litre bucket, then draw a line at that point and fill to there using the 3 litre bucket as a source.
so we have the OP solution: ask someone on PF

and the caveat emptor solution: kholdstare's split the difference

and the greek solution (compass and straight edge only): mine

and the high-tech engineering solution: Danger's

we still need a management solution and a CEO solution to complete the picture.

Of course VP Biden could step in at anytime with a shotgun solution but we won't consider that option for now :-)

Curious3141
Homework Helper
so we have the OP solution: ask someone on PF

and the caveat emptor solution: kholdstare's split the difference

and the greek solution (compass and straight edge only): mine

and the high-tech engineering solution: Danger's

we still need a management solution and a CEO solution to complete the picture.

Of course VP Biden could step in at anytime with a shotgun solution but we won't consider that option for now :-)
Management solution: Set up an interdepartmental cross-disciplinary committee with broad terms of reference to study the problem. Outsourcing is an acceptable option, preferably to a third world country where buckets, natural water sources and cheap labour are already plentiful, obviating the need for a budget to procure these.

CEO solution: CEO admits to not being able to solve the problem, and not even having foreseen that such a problem might exist. Therefore, regretfully, the CEO immediately resigns, accepting the previously agreed-upon golden parachute to the tune of \$50 million USD and another plum CEO job offer in a rival company.

Danger
Gold Member
I will mention two caveats to my answer.
1) It was partially a management response because there is no need for the 3-litre bucket, but since it's there it must be used.
2) It was purely theoretical because I have absolutely no idea of how to do the math.

Office_Shredder
Staff Emeritus
Gold Member
The Apple solution is to insist the 3 liter bucket is good enough and if you aren't getting 4 liters of water from it it's because you're holding it wrong

Curious3141
Homework Helper
The Apple solution is to insist the 3 liter bucket is good enough and if you aren't getting 4 liters of water from it it's because you're holding it wrong
They also insist that you fill it only with AppleTM water otherwise all warranty coverage on the bucket is void.

Danger
Gold Member
if you aren't getting 4 liters of water from it
But that won't happen.

ImATrackMan
They also insist that you fill it only with AppleTM water otherwise all warranty coverage on the bucket is void.
Using a special hose attachment that splits the stream and shapes it into two hexagons because, for whatever reason, a standard "circular" stream isn't as efficient.

Danger
Gold Member
Using a special hose attachment that splits the stream and shapes it into two hexagons because, for whatever reason, a standard "circular" stream isn't as efficient.
Do I see a patent for a spin-off from condom technology in your future? Maybe a urinal-based game of some sort?

You have got two buckets of capacity 3 litres and 5 litres each and a tap. How will you exactly measure out 4 litres of water with the help of two buckets and the tap.

Curious3141
Homework Helper

I thought of this movie too - I remember this scene very well (along with the Saint Ives riddle).

There are multiple solutions, of course. I think I found 3.

ImATrackMan
Do I see a patent for a spin-off from condom technology in your future? Maybe a urinal-based game of some sort?

pffft... no! Whatever could have made you think that? :uhh:

Danger
Gold Member
Whatever could have made you think that? :uhh:
Nothing in particular. My mind wanders sometimes...

ImATrackMan
Also, one solution.

Fill the five liter bucket completely

Pour out three liters (where else?)

Fill the 5 liter bucket to twice the level of the remaining water (assuming it's perfectly cylindrical).

Danger
Gold Member
That's pretty clever, Mr. Trackman, but... have you ever seen a cylindrical bucket?
My uncle owned a bucket store... I had to make buckets every day after school... we made wood buckets and steel buckets and I even made one out of a dead badger once... and I gotta tell you that not a single one of 'em was cylindrical.

ImATrackMan
That's pretty clever, Mr. Trackman, but... have you ever seen a cylindrical bucket?
My uncle owned a bucket store... I had to make buckets every day after school... we made wood buckets and steel buckets and I even made one out of a dead badger once... and I gotta tell you that not a single one of 'em was cylindrical.
The internal (or external, for that matter) shape of the bucket was never specified, though!

Danger
Gold Member
Oh, sure... get technical about it...

fill up the 3 liter bucket, pour it into the 5 liter bucket, then fill up the 3 liter bucket again and pour it into the 5 liter until the 5 liter bucket is full. Empty the 5 liter bucket pour the remaining 1 liter from the 3 liter bucket and then fill the 3 liter bucket and fill the 5 liter bucket, the water in the 4 liter bucket is exactly 4 liters.

DaveC426913
Gold Member

Using decanting principles.
As this is a well-understood method for solving such a problem, the details are left to the reader.

davenn