Wednesday 28 May 2014

The Friday Puzzle


Every Friday I put together an email entitled the 'Friday Report' which I send round to all of my teams. In it I include relevant articles and blog posts of interest to the various roles within the teams, including testing, documentation and support. As well as these links I also try to include a puzzle for people to tackle.

The original intention of including a puzzle was, as one might expect, as a bit of fun to encourage people to discuss the problem and find a solution. As I researched and presented more puzzles I started to see the scope for a less obvious, yet potentially more valuable benefit to these. I found that the most interesting discussions around the puzzles arose when individuals move beyond searching for the expected answer and start to apply critical thinking around the premises of the puzzles themselves. Through some simple questions I've been able to encourage some excellent debate around the puzzles themselves, calling into question the validity of the assumptions, the integrity of the constraints, and the viability of the solutions themselves.

  • Is the puzzle logically sound?
  • is the solution "on the card" the only one that fits?
  • Is it possible to come up with a different solution if we remove the assumed constraints?

Puzzles share many common characteristics with the situations that we are presented with working in a software company. They are usually based around some simplistic model of the world and the individuals within it that restrict behaviour, in a similar way that behaviour is modelled when developing software solutions. Puzzles may be presented with a limited set of information on the scenario in question, just as problems requiring diagnosis are rarely presented with all of the salient facts up front. Puzzles are presented with carefully chosen language to lead or mislead, just as customers, suppliers and other parties we interact with may sometimes use language to define their problems with the intention of leading us to the conclusions that they feel are relevant. In questioning the puzzles we are practising valuable skills in critical thinking that can be applied directly in our working contexts to ensure we maintain an open mind and consider options beyond the obvious ones presented to us.

I'm really pleased how enthusiastically everyone tackles these puzzles. On most Fridays now the discovery of the given answer is only the beginning of an excellent display of questioning and critical thinking around the problem. I've included here a few choice examples of puzzles and subsequent discussions that I think exhibit the exact characteristics that I'm really hoping for in this kind of exercise.

Choose your execution

This was the first puzzle in which I really started to see and introduce the idea of questioning the integrity of the puzzle itself as opposed to simply looking for the 'correct' answer. The interesting thing here is that the basis of the puzzle is that the prisoner escapes through manipulating the logic of his situation, however for me the language of the puzzle scenario provided scope for exploring other ideas.

Puzzle: General Gasslefield, accused of high treason, is sentenced to death by the court-martial. 
He is allowed to make a final statement, after which he will be shot if the statement is false 
or will be hung if the statement is true. Gasslefield makes his final statement and is released. 
What was his statement?**
  • A: I think the General said “I’m going to be shot”.*
  • Me: Well done, that’s the solution given. I personally would not have let him go – anyone see a way round letting him go?
  • J: Yes – I don’t see any reason why the alternative to “shot” or “hung” had to be “set free”. That’s not stated anywhere. It could have been continued incarceration – or some other method of execution. Anyway, given the statement, as soon as you take one or other of the two prescribed actions, either the statement or the action becomes invalid under the rules. If you don’t take an action, then we don’t yet know whether the statement is true of false – so he could continue to be held.
  • Me: They say they’ll shoot him if his statement is false but don’t explicitly say they won’t shoot him if it is true (i.e. it is an OR not an XOR) I’d have hung him then shot him.
  • S: Or may be shoot him on the leg and then hang him.

The Smuggler

This is a great example of something that is seen a lot in software circles. A solution that, on first examination, appears plausible, but that does not stand up well to closer scrutiny considering the practicalities of the situation.

A man comes up to the border of a country on his motorbike. He has three large sacks on his bike. The customs officer at the border crossing stop him and asks, “What is in the sacks?” 
“Sand,” answered the man.
The guard says, “We’ll see about that. Get off the bike.”
The guard takes the sacks and rips them apart; he empties them out and finds nothing in them but sand. He detains the man overnight and has the sand analysed, only to find that there is nothing but pure sand in the bags. The guard releases the man, puts the sand into new bags, lifts them onto the man’s shoulders and lets him cross the border.
A week later, the same thing happens. The customs officer asks, “What have you got?”
“Sand,” says the man.
The officer does another thorough examination and again discovers that the sacks contain nothing but sand. He gives the sand back to the man, and the man again crosses the border.
This sequence of events repeats every day for the next three years. Then one day, the man doesn’t show up. The border official meets up with him in a restaurant in the city. The officer says, “I know you’re smuggling something and it’s driving me crazy. It’s all I think about. I can’t even sleep. Just between you and me, what are you smuggling?”
What was he smuggling?
  • A: Smuggling gold dust in the sand?
  • L: I think he’s smuggling motorbikes.
  • Me: That is the 'answer on the card' - he was smuggling motorbikes. Any flaws in the puzzle?
  • O: Finding pure sand seems amiss as sand has absorbing properties. The analysis should have uncovered the sand plus all that it had absorbed e.g. water, sack fibre etc.
  • N: Surely the border guard would have noticed that it was a different bike each time?
  • S: could be the same model/colour with false number plates?
  • A: The official must have been suspicious if he was riding what appeared to be the same bike for 3 years but not showing any signs of wear and tear
  • S: He drove at night time; with poor lighting :)
  • Me: If he was smuggling motorbikes into the country - how did he get back? Would the lack of a motorbike on the return journey not have triggered some suspicion?
  • N: Maybe he smuggled cars or bicycles in the opposite direction? Or maybe he came back by bus or train.
  • S: The customs officer won’t be working 24 hours, so on his return on foot, a different officer is working and always sees him on foot.
  • Me: So the guy goes across every day and the customs officer is convinced that he's smuggling something to the extent that it is "driving him crazy" - but he doesn't tell his colleagues to check how the guy gets back and what he has with him? I wouldn't want to hire that customs officer for anything important.
  • S: We know little about him coming back – maybe he is doing the same in reverse…..(different model/make) and the customs officers did talk about it, but the ‘crazy’ one assumed it would be the same bike.

Predicting the score

This is a great example of a puzzle that is trying so hard to be clever that it has omitted the glaringly obvious, that the simplest answer may just be correct. Also included for a great piece of lateral thinking in the final response which is actually more pleasing than the rather unsatisfactory answer on the card.

Bill bets Craig £100 that he can predict the score of the hockey game before it starts. 
Craig agrees, but loses the bet. Why did Craig lose the bet?
  • S: Because the score of a hockey game before it starts is 0:0
  • Me: That's the answer on the card - everyone happy with that?
  • W: Because Bill guessed the correct score.
  • Me: That is some seriously twisted lateral thinking.
  • J: You can predict anything. Bill predicted the score. He didn't bet he would predict it correctly.

The Woman with half boys

This is a great example of where the language of the puzzle included unintended ambiguity. The answer on the card is based on an unsatisfactory premise that you can have half a boy. In this case, as with the previous one, I think that the team came up with a fast more elegant solution than the answer on the card.

 A woman has 7 children, half of them are boys. How can this be possible?
  • A: Maybe “half” means at least half, in which case she has at least 4 boys. Maybe she is expecting another one but doesn’t know the gender, so 4 of the 7 are boys, 3 are girls, and the one on its way could be either.
  • J: The statement is only that half are boys, there's no saying what the other half are - they could be boys too. If so, half are boys, a quarter are boys - any fraction. However, half of 7 of anything seems odd when the individual items are logically indivisible. Of course it could be in a specific application of the term "boy". So if one of the woman's children was a man or a woman rather than a boy, that could leave 3 and 3 boys and girls. That seems really inconsistent, though - being pedantic about "boy" but loose with "children" (and indeed loose with "them").
  • J: The "them" could include the woman, at which point, there are 8 people and if 4 are boys we're there.
  • Me: Well done J for coming up with an answer which, in my opinion, is actually neater than the one on the card (which was that they were all boys)

Carrying Sacks

This one I chose specifically due to ambiguity in the question that I thought would prompt interesting debate. It is a poorly worded puzzle and the team had no problem in dismantling it, and interestingly using it as an opportunity to explore the socio-political implications of the problem scenario!

A farmer and his hired help were carrying grain to the barn. 
The farmer carried one sack of grain and the hired help carried two sacks. 
Who carried the heavier load and why?
  • A: The farmer… the hired help had empty sacks… well it doesn't specify there was grain in them.
  • N: Even if there WAS grain in the hired help’s sacks, it would depend on how much grain was in each sack. So it could be either of them.
  • S: "A farmer and his hired help were carrying grain to the barn." This suggests that both were carrying grain. We don’t know the size or content of the sacks, or the weight of an empty sack. As it stands I do not think we can tell.
  • A: My thoughts exactly. Or maybe they were carrying different types of grain that weighed different amounts. Or maybe one was carrying dry grain and one was carrying waterlogged grain. Without further information it’s all just guesswork!
  • L: I’d hope that if the farmer had paid the guy, the hired man would have been of some help so therefore should be carrying at least as much weight as the farmer.
  • N: Depends what he or she was hired for. It might have been to feed the chickens and collect their eggs.
  • Me: Well done to N and L for getting the answer on the card. I'm with S and N - the first sentence states that they were both carrying grain. The second does not exclude the possibility of the hired help carrying grain, so the question is ambiguous and unanswerable. For me the most sensible answer is the 'obvious' one that the hired help carried more as the probability is that the sacks were full and of equal size, and as L points out, he was hired to help not just mess about with sacks.
  • E: But isn’t it more of a political/economic/philosophical question? The “hired help” represents the oppressed masses, forced to sell their labour for little or no reward. The “farmer” represents the capitalist oppressor. The burden of the hired help will always be the greater, in the exploitative capitalist society in which the farmer and the hired help notionally co-habit. My only question is why the farmer is carrying anything at all.

Riding into the Forest

Another one where the simplistic model of the problem doesn't stand up to practical considerations. Whilst something of an easy target, I really like the answers here.

How far can a horse run into a forest?
  • N: The answer to the puzzle is “half way”. Any further and the horse will be running OUT of the forest.
  • M: Depending on the density of the forest, I’d have to say “as far as the first tree”
  • Me: N has the answer on the cards, although Michael has applied some practical considerations to the issue….any other thoughts?
  • S: With regard N’s answer, that assumes the horse is running in a
  • straight line. It might be going in circles. A few answers from me:
    • As soon as it crosses the boundary into the forest, it is in, so it can’t run into it any further.
    • Until it stops running
    • Until it runs out of the forest
  • N: If the horse was riderless, it probably wouldn’t run into the forest at all. It would run over open ground if it could – less hazardous!
  • L: I agree with N - if a horse was riderless, it would not run through a forest. It would walk. Unless it was being chased, at which point I guess the answer is ‘until it got eaten’.

A Valuable Distraction

Whilst you could argue that these exercises distract from 'real' work I think that they are invaluable in promoting team debate around a subject and, more importantly, engender a team culture of collaborative criticism. I believe in encouraging an environment where it is acceptable to question the invisible boundaries that may have been established. Whether through our own assumptions or the dictate of others, were are often faced with the situation where we are introduced to scenarios with pre-established constraints, and the easiest option is usually to accept these and operate within them. I hope that by practising the process of questioning the scope and boundaries of every situation helps to ensure that we don't just blindly accept the information presented to us. I don't want to work with testers who only look for problems in the functionalities presented to them, I want to work with testers who question the functionality itself. I want to work with support agents who question the conclusions on that have been made by customers on what has caused the problems that they are facing. I want to work with technical authors who question behaviour and how it fits with the product set as a whole rather than simply documenting what has been done. Luckily for me that is exactly what I have, something I'm reminded of every Friday.


Some nice puzzle links can be found here:-


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