589: Designated Drivers

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Designated Drivers

Title text: Calling a cab means cutting into beer money.

Explanation

When a group of people go together to any kind of event where they expect to drink alcohol, and would like to drive to and from the event, it is usual to select one who has to be the designated driver. This person will then stay sober during the event, and can thus safely drive the other people home afterwards disregarding how drunk the other people becomes.

However, as this comic points out, if it not a simple task of going from A to B and back, all together at the same time, then it becomes an complex problem that requires an intricate kind of strategy and logical thinking to solve. And may need more than one driver.

In this comic Cueball addresses his friends, (Megan and two other Cueball-like guys), regarding this problem right before they enter a bar. It seems they have already decided that one of the friends (Tom) will be the designated driver. But then Cueball mentions that they will have to leave in two groups. And for some reason one of these groups will need two drivers (this is hard to explain?) So now they already need three designated drivers. Furthermore someone has to go and pick up Paul. (This could be one of the designated drivers though). And also two girls (Julia and Emily) has to leave earlier than the rest by 10:00. (That should then be be one of the two groups that Cueball mentions).

In the third panel the situation seems to be illustrated. Three people are drawn outside the bar with three lines going to the bar, so the number of lines leaving and entering each destination seems to represent a person each. Since the number of people leaving and entering each destination is the same, this makes it seem like the diagram is intended to be accurate. There are four people entering and exiting the bar and six people entering and exiting both the party and the dinner. The confusing part of the diagram is that it seems that someone will go back to the bar and another back to the dinner from the party. It is thus not easy to make the diagram fit the description.

Since the first panel must take place before any drinking takes place, to make the title of the comic make sense, then there is already missing one from the bar as we know that there are four at the bar at this moment. To make the diagram fit the fourth person should then be the one coming from the party. But he would thus come from there before anyone else arrived at the party. And then someone will have to leave directly from the bar without going to the dinner or party, since no one will come back later. And since Julia and Emily leaves together, this cannot be either of them. That would also mean that only five leaves the party since one of the leaving arrows was the fourth to get to the bar early. And there are six arriving, all of which must be assumed to arrive later yet. And since no one enters the party from outside, someone must have been at the party site from the start and would stay there afterwards. All this makes very little sense, so in the end it is not likely that the diagram in any way can represent the situation precisely.

But the general concept would be that some people meet at a bar before joining the rest of a group at dinner, then later most of these move on to a party. After the party (or bar/dinner) people are going to head home in different groups.

The enormous complexities of planning who car pools with whom, from where to where, and when, make an excellent logic puzzle. And what is worse, anyone who has to drive needs to stay sober. So it is important to solve the puzzle before the drinking starts.

To make matters worse the last Cueball-like guy complicates this already complicated logical puzzle, by involving the classic logic puzzle of the wolf, goat and cabbage. In the last panel the guy is shown standing with a goat on a teeter, saying he can't be in the car with the wolf. Cueball is then brought to swearing over this. (The goat puzzle was also the subject of 1134: Logic Boat).

The title text makes it clear why ordering a Taxi is out of the question as it would take money out of the beer budget. Of course it also cost money to use your own car for gas etc. But when you already have a car, it is always cheaper to use that than pay for a taxi.

Transcript

[Four people are outside a bar.]

Man: Wait, who's driving?

Friend: Why?

Friend: Tom, right?

Man: Yes, but we have to leave in two groups. One of which will need at least two drivers.

[There is a complicated flowchart with arrows between a group of people and 3 locations, labeled 'bar', 'dinner', and 'party'. Lines point from the group of people to the bar, then to the party or dinner, then from dinner to the party and vice versa, as well as leaving the panel or entering the panel in several other directions.]

Someone has to get Paul, and Julia and Emily have to leave by 10:00.

The logistics of who can get drunk are nontrivial.

[Cueball has an animal on a string behind him, which was previously not visible.]

Cueball: Yeah, and I can't ride in a car with the wolf because he'll eat my goat.

Man: Dammit, guys.

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Discussion

I think I read a reference to the goat/wolf puzzle in an older comic. 108.162.212.196 18:08, 1 January 2014 (UTC)

Why no explanation of the third panel? Is it because it doesn't make sense? That seems unlike Randall, so I'll have a go.

Proposed Order of Events:

• On the diagram, we see three figures entering the bar, and three lines entering dinner (probably Paul, and Emily and Julie). That makes six people altogether.

This makes no sense as there are four at the bar to begin with. Also one of the people already there would have to go and pick-up Paul and thus arrive at the party with him (two lines entering). Since Megan could be one of the two girls, the last girl could be the one arriving alone. But the above takes the first Cueball out of the equation! Thus if what I wrote here is true, then all the rest of this explanation below falls --Kynde (talk) 19:17, 31 October 2015 (UTC)

• Of the three at the bar, two go to dinner and one goes straight to the party
• All five people leave the dinner and go to the party, joining the sixth.
• Two of the six leave the party together (Julie and Emily at 10pm)
• One of the six leaves the party and goes back to the dinner venue, and from there goes home.
• One of the six leaves the party and goes back to the bar
• The last two leave the party and on their way home, appear to join up with the one who went back to the bar

Because there are no times or identities assigned to the paths, other interpretations are possible.

Notes:

• The diagram as a whole has six entries and six exits, as does each venue. There are definitely six people who all enter from the outside, and eventually leave.
• Why are there four people visible in the first panel, but only three people start at the bar? That part makes no sense. To match the diagram to the comic, we have to pretend that there are only three people in the first panel.
• Who is Tom? He must be one of the people visible in the first panel, even though he is spoken about as though he wasn't there.

Ignoring the goat for now, how many drivers do we need?

• Most cars can take five people at a pinch, so sheer numbers don't seem to be the issue.
• You need two drivers (and two cars) if people were leaving at different times, or heading in entirely different directions.
• Presumably, Julie and Emily arrive in their own car and also leave in it. Ignore them for now..
• Someone drives back from the party to the dinner, and then home. This must be one of the people from the first panel, and they must have their own car.

Proposal:

• There are only three people at the bar, Tom, Megan and (I'll say) David. They each have their own car.
• David drives to the party. Tom and Megan drive separately to the dinner, one of them collecting Paul on the way.
• Tom and Megan drive from the dinner to the party; Paul rides with one of them.
• Megan later drives back to the dinner venue, then home.
• Paul later drives Tom's car back to the bar, and proceeds to get drunk.
• David drives Tom a ride to the bar, to collect his car and drive Paul home.

Note that this scenario implies that everybody who is initially at the bar has to be a designated driver.

And I have still not considered the goat.

Any other interpretations would be welcome! I am not really satisfied with this but got tired of thinking about it.108.162.219.58 18:52, 7 February 2014 (UTC)

tl;dr or Wikipedia:Too long; didn't read. Please calm down just to the essentials. And please try to keep an explain just straight forward. --Dgbrt (talk) 21:08, 7 February 2014 (UTC)

I have made a suggestion that could explain the information and the diagram, but it assumes that the party is held at Cueballs place (the one who talks first). And that he starts and ends there. The three drivers is though not easy to explain. --Kynde (talk) 19:17, 31 October 2015 (UTC)

<sigh> everyone forgets the cabbage... Brettpeirce (talk) 15:12, 27 February 2014 (UTC)

- For those unfamiliar, the goat/wolf reference is an old logic puzzle. You have a goat, wolf and head of cabbage. Using a rowboat, how can you get them all safely across a lake? Sometimes the assumptions are given: Goat eats cabbage, Wolf eats goat. Sometimes only 1 item at a time in rowboat, sometimes two. Solve. (Goat, empty, ...)

- BTW, I think the diagram description above is ok, shows how lots of interpretations possible. If it is inaccurate, well, has the artist already been to the bar? Arranging outings with friends, sometimes it's just a hassle, eh? And people will try to solve problems with the tools they know, hence a flow-diagram from the head XKCD geek. Just needs a state table with optimizations to make it complete! (-: 199.27.128.114 18:25, 9 June 2014 (UTC)

I like the double meaning of "non-trivial" in the comic. There's the math sense of the term and also the human sense. To fully appreciate the human sense it helps to be old enough to know that, say, 35 years ago, drunk driving was commonly regarded as a trivial problem. MADD (Mothers Against Drunk Driving), founded in 1980, helped change this, as did increasingly drastic penalties and public shaming of people who drove drunk. When I was growing up (1960s) and a young adult (1970s) there was no concept of Designated Driver. Npsych (talk) 09:52, 9 October 2015 (UTC)

I believe the reason one group needs two drivers is that said group may be due for a longer, cross-continental trip (and driving hung over with minimal sleep in a sedan isn't much easier than driving drunk)... Maybe we finally solved anothe logic problem? Papayaman1000 (talk) 03:22, 6 March 2016 (UTC)

Just overhauled the last two sections. If anyone has anything to add or I made a mistake in my solution, I'd love to hear feedback on it. Toadfart (talk) 21:46, 14 September 2016 (UTC)