Missing dollar riddle

One of my favourite puzzles is this one, from the 1930s:

Three people check into a hotel room. The clerk says the bill is $30, so each guest pays $10. Later the clerk realises the bill should only be $25.

To rectify this, he gives the bellhop $5 to return to the guests. On the way to the room, the bellhop realises that he cannot divide the money equally. As the guests didn’t know the total of the revised bill, the bellhop decides to just give each guest $1 and keep $2 as a tip for himself.

Each guest got $1 back, so now each guest only paid $9, bringing the total paid to $27. The bellhop has $2. And $27 + $2 = $29 so, if the guests originally handed over $30, what happened to the remaining $1?

Try to solve this without any further hints.

Obviously, there’s a trick.

The misdirection in this riddle is at the end of the description, where a bunch of unrelated numbers are added together – only to misguide the listener.

There’s no reason to add these random totals, and even less reason for the sum to add 30. If you wanted to sum up the cash total, you have to look at the $25 in the register, the 3*$1 in the guests’ pocket, and the $2 with the bellhop. That’s, as expected $30.

More missing dollars on Wikipedia.

j j j

The Pleasures and Pains of Coffee

The state coffee puts one in when it is drunk on an empty stomach under these magisterial conditions produces a kind of animation that looks like anger: one’s voice rises, one’s gestures suggest unhealthy impatience: one wants everything to proceed with the speed of ideas; one becomes brusque, ill-tempered about nothing. One actually becomes that fickle character, The Poet, condemned by grocers and their like. One assumes that everyone is equally lucid.

A man of spirit must therefore avoid going out in public. I discovered this singular state through a series of accidents that made me lose, without any effort, the ecstasy I had been feeling. Some friends, with whom I had gone out to the country, witnessed me arguing about everything, haranguing with monumental bad faith. The following day I recognized my wrongdoing and we searched the cause. My friends were wise men of the first rank, and we found the problem soon enough: coffee wanted its victim.

— Honore de Balzac: The Pleasures and Pains of Coffee

j j j

One happy vagina

On this photograph below, yours truly is smiling.


The picture was taken somewhere in Shoreditch, the “Making Vaginas Happy” sign belongs to some organic feminine care creme that women apply, you know, on their private parts mostly.

Anyways, I don’t share much stuff on social media, but I thought: this is a great picture. I’m proud of this one. I smile and everyone can see that I still have all my teeth.

I will share this.

And then, a few hours later I realised that my girlfriend’s dad is a friend of mine on Facebook. I realised this because he commented on the photo.


Oh boy.

j j j


One team I’m working with is 100% proper nerds. Imagine a transportation consultancy where people work with massive data models and advise governments, mayor’s offices or public events. To illustrate, one project we’ve worked on is the Champions League’s finals in Cardiff.

Definitely real nerds then. Not completely unlike Big Bang Theory but not exactly the same either. You definitely see more white ironed shirts than Google hoodies, but people are surely very much interested in what they do.

Trainspotters - Frederique comics

There’s a new project coming up, and on the kickoff meeting in the Bankside office I see consultants I haven’t met before. They are just as well: nerds, but you know, I too have studied maths for over 20 years. I can relate.

The meeting goes well, and I’m leaving the room with a friend who’s with the company for a longer time.

“Wait till you know these guys better”, he says. “They are nerds.”

“What do you mean they are nerds? You guys all are!”

“No, they are proper nerds. They are going-train-spotting-together level of nerds. They do actually: go out, watch trains, knowing exactly which service those are.”

Can’t wait for this project to get started!

j j j

Diversity is strength

My girlfriend introduced me Taqanu founder Balazs Nemethi, because, well first, she knows that I’m best kept around fellow entrepreneurs and Balazs is great fun, and second, their bank-for-refugees startup is a great fit for our magazine Yakuzuzu. This post is excerpt from the interview that followed.

YZ: How was life in Norway? What did you learn there?

Norwegians are great at keeping a healthy work-life balance. They would work hard for eight hours, but then they would go home and hang out in front of the fireplace for the evening. This is something I try to take with me from those days: I try to keep one day a week when I do absolutely no work at all. It’s great for new ideas.

I’m not so great at this, sometimes I get stuck in work-mode for ways too long, but then my friends intervene: if I’m not responding for a few days, they would start writing me texts like “hey, it’s Tuesday night, stop working!”

YZ: How did you stumble upon the Taqanu idea?

The point with finding any project in Norway was to be distracted from reality. I was on the market for something with the promise of keeping me excited during the evenings: a project that’s bigger than you are.

It took some corners to arrive at Taqanu. I was interested in blockchain and banking, and explored ideas in that area. Plus, I was in Norway and I’m Hungarian, and then, in the Summer of 2015 Hungary built the wall to keep refugees out. All the people I’ve met in Norway asked about this one thing: how is it with Hungary and the wall? I tried to explain that it’s not like everyone in Hungary would want to keep the refugees out, most of us are in fact nice people.

These chats around the topic helped a lot to discover the utility in a digital fingerprint, and so the idea was born. I started to work on Taqanu.

It all started as project to offer banking services for refugees. Now it’s been developing into a global solution for decentralised identification and an answer to the lack of access to financial services for the estimated two billion people without financial opportunities.

YZ: What’s the next step after the idea is born? How did you get started?

I went to blockchain meetups in Oslo to pitch the idea. I had great experience there, the success started to knock on the door pretty early.

Taqanu was one of the few selected startups in the first Nexuslab programme. In cooperation with the London startup accelerator Startupbootcamp Fintech, Nexuslab gave us mentorship and coaching sessions for three months. There was only a small glitch: the final month of the programme was held in Zurich. I didn’t think twice, quit my architect job in Norway, and started to pack my bags.

The programme was great, Taqanu was taking shape, and I was talking to people who previously seemed to be way out of my league. I was invited to be a panelist on the “Proof of Identity for Refugees and Beyond” discussion on the European Identity & Cloud Conference in Munich, talking about blockchain based supranational identity infrastructure with people like Kim Cameron, Chief Architect of Identity at Microsoft or Mia Harbitz, advisor at the World Bank Group.

The story continues on Yakuzuzu.

j j j

What’s next to my bed?

I woke up for someone standing next to my bed. For real.

It’s an Airbnb with two rooms rented out: us in one, another couple in the next. The guy from the next room got confused when returning from a nightly toilet run, took the wrong turn and somehow ended up standing next to me when I was asleep.

If you’ve never had to wake up for a stranger standing next to you and trying to recognise your shape in the dark, well, it doesn’t feel very good.

Those nightmares when aliens gather around your bed while you’re asleep and paralysed, and then all sorts of shit happens.

The all sorts of shit in this case was mostly, someone with an Italian accent saying “Fuck I’m sorry I’m so sorry sorry I’m sorry” and rushing out of the room.

Which is all my girlfriend could remember of the next morning: some weird mumbled Italian swearing.

It might very well have been me.

j j j

Compare it with being dead

I’ve overheard someone comparing washable diapers with the non-reusable ones. One supposed to be environment friendly and the other less so.

In the comparison the washable diapers were almost free from all environmental damage. Which would obviously only be true if you skipped the washing bit of the reuse.

If you haven’t heard of the Penny lick ice cream glasses: in the 1800s London, one happy customer would get their ice cream, lick the glass clean and return it to the vendor, who would refill it and give it to the next customer. Apart from being yuuuck, this is perhaps the best way to spread tuberculosis, which the Penny lick did very well on until it was banned in 1899.

Don’t skip the washing bit when reusing a diaper, it’s super-ill-advised.

However, washing a reusable diaper makes the whole thing very unfriendly to the environment. When you compare the two options, apples-to-apples, you’re only choosing between the lesser of two evils.

This was a cafe chat that I’ve overheard and this is a Friday morning, so clearly we are not expecting scientific evidence. Also, I love when something is environment friendly and I’m on the same side: I too want the reusable stuff to win. But, for a mathematician, it’s nice to have the facts straight.

People don’t cheat when comparing stuff on purpose, and I’m certainly no exception. Humans are generally not good at rational reasoning.

Like now, I want to think that all this cappuccino will disappear if I swim for an hour. Sports are a great way to burn a gazillion calories.

Do you know how many calories would I burn simply standing still instead of swimming? Surprisingly, still quite a lot. Simply living-and-breathing consumes almost the same amount of calories as swimming for the same period, the difference is only some 20%.

Turns out that people mostly compare calorie consumption during sports with: being dead.

j j j

Not news

Both Berlin airports were shut down for 24 hours last Friday. No flights in-or-out of the German capital for a whole day, but I only know this because my girlfriend was lucky enough to be on the last Berlin-London flight before they closed the airport for the strike. The news outlets were pretty silent.

This week then, now for two consecutive days, both airports were shut again on Monday and Tuesday. No flights in-or-out of Berlin, again, for 48 hours.

Shouldn’t it have been covered in the news somewhere? I’ve seen it on Reuters and Twitter, but really, nothing on CNN and BBC.

I mean, this is the Germany capital being cut off the maps for all international and domestic airlines for 3 whole days now, with thousands of flights cancelled, and BBC doesn’t seem to care about it. The German Zeit doesn’t care much either.

Is it only me who’s missing this in the news? Or is this uninteresting and all people care about is random boobs and futballists?

j j j

Surely You’re Joking

“Well, Mr. Frankel, who started this program, began to suffer from the computer disease that anybody who works with computers now knows about. It’s a very serious disease and it interferes completely with the work. The trouble with computers is you play with them. They are so wonderful. You have these switches – if it’s an even number you do this, if it’s an odd number you do that – and pretty soon you can do more and more elaborate things if you are clever enough, on one machine.

After a while the whole system broke down. Frankel wasn’t paying any attention; he wasn’t supervising anybody. The system was going very, very slowly – while he was sitting in a room figuring out how to make one tabulator automatically print arc-tangent X, and then it would start and it would print columns and then bitsi, bitsi, bitsi, and calculate the arc-tangent automatically by integrating as it went along and make a whole table in one operation.

Absolutely useless. We had tables of arc-tangents. But if you’ve ever worked with computers, you understand the disease – the delight in being able to see how much you can do. But he got the disease for the first time, the poor fellow who invented the thing.”

— Richard Feynman in the book “Surely You’re Joking, Mr. Feynman!: Adventures of a Curious Character”

j j j