[engineer question] coins

[martyr]

this isnt as hard as rope part 2, which smaug defeated.

the accepted answer for this is different than the one i came up with, and i know of another - there are options here.

also, this question is designed to generate dialogue with the interviewer, as though you were troubleshooting a software problem.



you have ten machines producing coins.
one machine is malfunctioning.
you may use a scale to weigh a mass only once.
determine which machine is malfunctioning.

[Baneblade]

Take the plates for the $100 bill and jump ship.

[Strygun]

what's the correct mass of a coin from a working machine?

[Strygun]

I've made another post because I bet you're reading the one i just made, and if I edited that, you wouldn't see it.

Are the coins from the working machines and the malfunctioning machine the same size? color? shape? density? combination of metal/metals?

[eXoSloth]

Go to the store and buy nine more scales...

[martyr]

the correct mass of a coin is 1g.

the coins from the machines are identical in all physical aspects except mass and density.

the malfunctioning machine is generating a bad alloy resulting in less mass but equal volume.

[Strygun]

what type of scale are we talking about here? a balancing scale, in that you place 2 coins on 2 sides and if they are good coins the scale will balance? or are we talking about a scale that measures mass?

[Indecisive]

Mass a coin, and compare it to the 9 other coins..how though. It would be friggen simple if you could weigh it multiple times

[Strygun]

are there other tools at our disposal? can we get other tools ourselves (within reason?)

[eXoSloth]

Put a coin from each machine in a bucket of water, the bad coin will float. (Maybe.)

[Strygun]

exo.. I dunno if we can use buckets of water but if we can, that was my idea first (I asked about density.)

[Strygun]

what is the mass of the bad coin?

[eXoSloth]

Originally Posted by Strygun

exo.. I dunno if we can use buckets of water but if we can, that was my idea first (I asked about density.)

It was our idea at the same time

[martyr]

triple-beam scale.



no other tools

[Baneblade]

By mass only once does that mean a single coin, or can you stretch it out to include all of them one at a time, just noting the difference.