Riddle

2020-02-29 (Leap day!)

Posted on by What did you learn in School today ?

Today, I learned about:

Exactly four years have gone since I last wrote about what a leap day is, 2016-02-29.

And here we are again, four years older, and maybe even wiser! I was thinking about the poor guy that was born on 1896-02-29. He celebrated his birthday on the correct date of the year only when there were eight candles on his birthday cake. How come? Well, as you know a leap year normally happens only once every four years, but when the century is on its first year, then it must also be evenly divided by 400, i.e. 1600, 2000, 2400 etc. But then, he knew that if he lived that long, he would still celebrate it on the correct day with 12, 16, 20, 24, … candles!

‘Can you use an hourglass’?

Finally, here comes the solution to the riddle posted back in 2019-12-31:

You start with two loaded hourglasses at the same time. After 7 min, when the small hourglass is done, you turn it over and restart it.

After 11 min, when the big hourglass is done, you leave it as it is. But now you turn over the small hourglass, which has had a second run of 4 min, and let it run for the third time until it stops.

Voilà, you have now accomplished the task!

That’s what I learned in school !

Ref.:

*: What did you learn in school today ?

2020-01-09 (4 years!)

Posted on by What did you learn in School today ?

Today, I learned about:

Exactly four years have gone since I wrote my first post in this blog, 2016-01-09. It was really short, talking about potatoes, but it gave me the kick to want more. The story about why I started the blog was published on 2017-01-14.

Thank you all who follow my blog and write me with suggestions about what to publish in future posts!

A hint to ‘Can you use an hourglass’?

In my most recent post, on 2019-12-31 , I gave you a problem involving the use of two different hourglasses, with capacity of 11 min and 7 min, respectively, and asked you to measure exactly 15 min.

If you are still fighting with the solution, let me give you two important hints:

11 – 7 = 4

and

15 – 11 = 4

Can you solve it now?

A complete solution will be presented in my next post.

That’s what I learned in school !

Ref.:

*: What did you learn in school today ?

2019-12-31 (Réveillon!)

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Today, I learned about:

Once again, it is that day of the year when we reflect over how the year behind us was and make our predictions and wishes for the year to come.

One important piece of news during 2019 was that researchers at my alma mater Chalmers University of Technology, Gothenburg, Sweden, led by professor Kasper Moth-Poulsen reported that they have developed a molecule, that is able to capture the sun’s rays, store it as chemical energy for up to 18 years, and retrieve the energy and convert it into heat when needed.

The following graphic shows how it all works:

It all starts in the upper middle section of the sketch. The solar reflector (SOLFÅNGARE) placed on the roof of a building captures the sun’s rays. The parabolic section concentrates solar energy and transmits it to the liquid in the tube in the center of the solar reflector. From there, the cold liquid, now containing stored chemical energy, is sent to an energy storage (ENERGILAGER). It can be stored there for up to 18 years! When we need to heat up our house, we simply let some of the liquid out from storage, run it through the catalyst (KATALYSATOR), thus obtaining a hot liquid without any stored chemical energy. Experiments have shown that the liquid with released heat can have a temperature that is 63 °C higher after the catalyst in relation to before! The hot liquid then goes into the normal heating system of the house, e.g. the radiators (ELEMENT I HUS) in the various rooms, heats up the ambient, and then the now cold liquid goes back up to the roof to capture more sun rays. Graphic made by Yen Strandqvist.
The leftmost photo shows the parabolic solar reflector with the liquid tube in the center. To the right is the inventor of the material, professor Kasper Moth-Poulsen, securing a small sample of the miraculous liquid. All material has been extracted from Chalmers Magasin no. 1 2019, text by Karin Aase and photos taken by Oscar Mattsson and Johan Bodell.

References # 1 through 4 below contain more material if you are interested in further details.

Can you use an hourglass?

According to Wikipedia: “An hourglass (or sandglass, sand timer, sand clock or egg timer) is a device used to measure the passage of time. It comprises two glass bulbs connected vertically by a narrow neck that allows a regulated flow of a substance (historically sand) from the upper bulb to the lower one. Typically the upper and lower bulbs are symmetric so that the hourglass will measure the same duration regardless of orientation. The specific duration of time a given hourglass measures is determined by factors including the quantity and coarseness of the particulate matter, the bulb size, and the neck width.

So you think are smart? Then show it now! We have two hourglasses like the ones shown above. The bigger ones completes one cycle in 11 minutes, the small one in 7 minutes.

Question: Using a combination of these two hourglasses, you need to measure a time lapse of exactly 15 minutes. How would you do it? (Solution to follow in the first blog post of 2020.)

I wish all my faithful blog readers a HAPPY NEW YEAR!

That’s what I learned in school !

Refs.:

1: Extract from Chalmers Magasin nr 1 2019 (article in Swedish)

2: An energy breakthrough could store solar power for decades

3: Storing the energy from the sun for decades

4: Liquid sunlight creates heat on demand

*: What did you learn in school today ?

2016-03-05 (Saturday)

Posted on by What did you learn in School today ?

Today, I learned that:

If I were in Northern Europe now, I believe that a typical Brazilian dish would be very welcome to keep the cold out.

In my post of 2016-02-14, I explained how to make a typical Brazilian drink called Caipirinha. And after one or a couple of those, when the stomach starts to rumble, what could be better on a lazy Saturday afternoon than a Feijoada?

feijoada

Complete Feijoada from Minas Gerais

Feijoada is a stew of beans (named “feijão” in Portuguese) with beef and pork, with origins in Portugal, but made famous in Brazil. It is a typical dish for lunch on Wednesdays and Saturdays, although eating it in the middle of the week can be too filling for many people, so they prefer to wait until Saturday, when they can also enjoy it without guilt after the Caipirinha. Reference #1 gives the basic idea of what is needed to compose a Feijoada, but if you want the whole story, look in reference #2 (in Portuguese), with gives all the details of how the traditional Feijoada is made in the state of Minas Gerais, such as in the photo above.

Solution to The fast mover, posted on 2016-02-27

The riddle read: What can go from there to here by disappearing and then go from here to there by appearing? Look at the phrase again, which is the difference between the words ‘there’ and ‘here’? Of course, the letter ‘t’, which is the solution to the whole riddle.

A new problem will be presented tomorrow!

Svaret på bonusfrågan om det falska körkortet är att det finns tre fel i personnumret, angivet såsom 660202-0001:

  • De tre siffrorna närmast efter bindestrecket, de sjunde till nionde siffrorna, måste vara en sekvens från 001 till 999, 000 finns ej. I äldre personnummer indikerar de sjunde och åttonde siffrorna i vilket län personen föddes, men det gäller inte längre.
  • Om vi kan anta att innehavaren av körkortet är man, vilket både namn och foto tyder på, så måste den nionde siffran vara udda. Jämna siffror, inklusive 0, är reserverade för kvinnor.
  • Även om de första nio siffrorna vore korrekta, så är den tionde siffran (kontrollsiffran) fel. Om vi använder  formeln i Skatteverkets informationsblad, referens nr 3, så skulle slutsiffran vara 7.

 

… That’s what I learned in school !

Refs.:

1: Feijoada explained in English

2: Feijoada mineira completa

3: Skatteverkets informationsblad om personnummer

+: What did you learn in school today ?

2016-02-27 (Saturday)

Posted on by What did you learn in School today ?

Today, I learned that:

The interest for solving riddles is big among my readers, and the first correct solution to The pill roulette was submitted by Barbara and her colleagues at Torpaskolan in Gothenburg, Sweden. Congratulations to all you clever people! And here comes the …

Solution to The pill roulette, posted on 2016-02-21

  • Divide the eight pills into three different piles, two having three pills each and one with two pills.
  • Place one pile with three pills on the left pan of the balance scale and the other pile of three pills on the right pan.
  • If the weighing results in equality, then we know that all those six pills are also equal and none is poisonous. A second weighing of the remaining two pills indicates which pill is the poisonous one, since it is a little heavier.
  • However, if the first weighing results in that the total mass (“weight”) of one pile with three pills is heavier than the other pile of three, then we know that both the lighter pile of three and the sided two pills are all normal pills without any poision. Thus concentrate on the heaviest pile of three, one of the pills in it is the poisonous one. Take any two of those three pills and place one each on either pan of the balance scale. If this second weighing results in equality, both of the two pills are OK, and the sided third pill is the poisonous one. But if one of the two pills on the scale is heavier than the other one, it is the poisionous one!

A new riddle can be found at the end of today’s blog.

The Internet of Things

Last week was a busy one in Barcelona, Spain, where the Mobile World Congress gathered many people to learn and spread the word about the current state of affairs. Today, I will restrict the field to the so-called Internet of Things (IoT), which is the increasing number of appliances, gadgets, vehicles, etc. that connect and interchange information. Radio Sweden’s weekly financial update was entirely dedicated to IoT, giving specialists from Ericsson, Huawei, Nokia, and Oracle a chance to share their thoughts. For the complete program, listen to reference # 1 below, but if you do not cope very well with the Swedish language, I will give you some of what was discussed here:

  • IoT has been around for quite a while, although in a unorganized manner, through all the sensors that have reported various parameter values to centralized locations, which evolved to machine-to-machine communication (M2M) and now IoT.
  • Built-in sensors in our homes will warn us when all is not the way it should be, e.g. if there are leaks of water, gas, etc., and instead of us having to call for someone to come and help us during normal business hours, we will receive a message telling us about the current situation and asking us about when that someone would be welcome to come to our home and solve the problem.
  • The self-driving cars will be upon us soon.
  • Provided that we can guarantee that the communications are resistant to hacker attacks, people are willing to share the biomedical data remotely. And the 5G networks that soon will be available are said to offer so much more security than today’s technologies, because already from the start 5G has been created to serve IoT well, and not be just another broadband communication technology.
  • A test with connected garbage cans in Germany, where the garbage only was collected when the cans called and informed that they were full, showed a 50 % reduction in costs in relation to the traditional scheduled garbage collections.
  • If we compare the development of applications for IoT between USA and Western Europe, then there is an interesting remark. Whereas the American development is more concentrated to big corporations, in Western Europe there are many small companies involved and their flexibility and speed can result in launches of new products well ahead of their American competitors. Furthermore, we can already see a trend where small European companies win over their Asian competitors in providing products in smaller volumes tailored to their customers’ needs.
  • I already talked about 5G in my post on 2016-01-24, citing applications that demand the high speed of a 5G network to function adequately. Look at references #2 and #3 below, where it is explicitly shown in text, photos and videos from Barcelona.
  • Our pets will inform us where they are, how they are, if they are hungry, etc.

hidog

Connected dog, sending messages from a display on the collar or via Internet of Things

Riddle # 3 (The fast mover)
What can go from there to here by disappearing and then go from here to there by appearing? A solution to this riddle will be published next Saturday, 2016-03-05. The first person that comes across the correct solution and sends it to medieborgaren@sjson.com will receive an honorary mention.

Slutligen, Ordalaget har gjort det igen! Igår gav de oss ett nyord för en falsk ID-handling, en s.k. legimitation.

Svenskt körkort

Bonusfråga: Även om texten “SPECIMEN” inte funnes, så vore detta ett utmärkt exempel på en legimitation. Kan du lista ut varför? (Svar kommer tillsammans med lösningen på gåta nummer 3 ovan 2016-03-05)

… That’s what I learned in school ! … Slut för idag, tack för idag !

Refs.:

1: Sakernas internet och framtiden

2: 5G was the real star of Mobile World Congress

3: A true 5G demo

4: Legimitation

+: What did you learn in school today ?

2016-02-21 (Sunday)

Posted on by What did you learn in School today ?

Today, I learned once more that:

One of the most abstract things in our world is also something that we rely on the most. I am thinking about the so-called fourth dimension, time. Due to the earth’s rotation around its own axis, the world has been divided into 24 time zones, with the meridian that crosses the Greenwich observatory in England used as a starting point for the division, and thus establishing Greenwich Mean Time (GMT), nowadays mostly named Coordinated Universal Time (UTC).

Due to its subcontinental size, Brazil has four different time zones, which are related to the official Brazilian time in the Federal capital of Brasília. The following times apply as standard times:

  • Brasília time – 2 h (UTC-5 h): State of Acre, and the Southwestern part of the state of Amazonas. The proportion of people living here is only 0,5 % of the country’s whole population (a little more than 1 million people). This time zone covers only about 6% of the Brazilian territory (although it is about the size of France).
  • Brasília time – 1 h (UTC-4 h): States of Mato Grosso, Mato Grosso do Sul, Rondônia, Roraima, and the rest (main part) of Amazonas. 5% of the country’s population live here (about 11 million people). The area is big, 34% of the land area of Brazil (thus larger than Argentina).
  • Brasília time, BRT (UTC-3 h): Federal District (which includes Brasília); and also the states in the Southeast Region ( Espírito Santo, Minas Gerais, Rio de Janeiro, and São Paulo); the South Region ( Paraná, Rio Grande do Sul Santa Catarina, and Rio Grande do Sul); and the Northeast Region ( Alagoas, Bahia, Ceará, Maranhão, Paraíba, Pernambuco, Piauí, Rio Grande do Norte, and Sergipe) as well as the states of Amapá, Goiás, Pará, and Tocantins. Almost 94% of the whole Brazilian population live in this time zone, which also covers about 60% of the country’s land area.
  • Brasília time + 1 h (UTC-2 h): A few small offshore Atlantic islands, namely Fernando de Noronha, with 2,837 inhabitants and 0,0014% of Brazil’s population, an the non-populated islands of Trindade, Martim Vaz, Rocas Atoll, and Saint Peter and Saint Paul Archipelago.

The reason I am mentioning this today is that yesterday at midnight in Brasília, some of the states mentioned above, namely the Federal District and the 10 Southernmost states (Rio Grande do Sul, Santa Catarina, Paraná, Mato Grosso do Sul, São Paulo, Rio de Janeiro, Espírito Santo, Minas Gerais, Goiás, and Mato Grosso) ended the period of Daylight Savings Time (DST), also called Summer Time, that had been valid since October 18, 2015. The population in those areas account for 64 % of the total Brazilian population.

DST was used in Brazil for the first time in 1931, but from then on there was no consistency in when it was applied. It was only in 1985 that DST was instituted and followed on a regular, annual base, normally between the third Sunday of October and the third Sunday of February the subsequent year. However, Carnival and general elections have influenced on different start and end dates on some occasions.

One interesting observation that can be made is that the change always happens around midnight Brasília time, which creates a big confusion about which day it is at a given time. To me, the European rule of making the change at 02:00 / 03:00 seems much more logical.

However, there are people that oppose to the use of DST. As an example, there are currently three different propositions in the Brazilian Congress that want to forbid the use of DST. One of those propositions was written by congress man Valdir Colatto from Santa Catarina. Here are his arguments:

  • An institute of cardiology performed scientific tests about how DST affects the people, and they found an increase in health problems, from hypertension to diabetes, sometimes also depression.
  • During DST, the children learn less in school, because they have to wake up earlier.
  • He normally needs to wake up at 04:30 on Monday mornings, so that he can take a plane from his home town, Chapecó, to Brasília an hour later. During DST, he has to wake up at 03:30 solar time, an hour earlier due to a decree from the President of the Republic.
  • He responds to the official argument, that the use of DST saves energy, that nobody notes that difference in their electricity bill.
  • According to him, a survey performed on the internet resulted in that 80 % of those that responded to the survey said that they were against the use of DST.

 

Solution to Riddle # 1 (Two blind men), posted on 2016-02-19

When the socks are sold in the store, they are also grouped together in pairs. Thus, it is easy to grab one pair, separate the socks and place one each in each of the two men’s bags. Continue doing so, and eventually you will have two blue socks, two red socks, two pink socks, two green socks, and two orange socks in each bag.

I have already told this riddle to many people, but only one person could ever solve it, and it took only 15 seconds! This is a tribute to my good old friend, the chemist John Snyder, one of the most intelligent people I know!

The riddle was first proposed by Kim Nasmyth, Professor of Biochemistry at the University of Oxford, to explain how chromosomes divide in cell division, see reference # 3 below.

Riddle # 2 (The pill roulette)

You suffer from a temporary disease, which you have to treat by taking one pill every day during seven days. So the pharmacist took your order and gave you the pills. You are just about to take the first pill, when you receive a telephone call from the pharmacy.

You are informed, that the attendent mistakingly gave you eight pills, the seven you need and also an eighth one, that has the same appearance as the other. But it is poisonous and furthermore it weighs a little bit more than each of the other seven, undetectable by assessing it in your hand, but sufficient to be determined by a precision scale.

Luckily, you are in a laboratory which has such a scale, an old analogue weighing scale with two pans for high precision weight measurement. The problem is that you will only be able to perform two measurements, after which the scales will not work any more.
Here is a drawing of the scales you can use:

two-pan-balance-scale

A two-pan balance scale to be used in riddle # 2

So how do you solve this riddle, to identify and discard the poisonous pill, with only two comparative measurements? A solution to this riddle will be published next Saturday, 2016-02-27. The first person that comes across the correct solution and sends it to medieborgaren@sjson.com will receive an honorary mention.

… That’s what I learned in school !

Refs.:

1: Time in Brazil

2: Horário de verão acaba à meia-noite deste sábado

3: How chromosomes split in cell division

+: What did you learn in school today ?

2016-02-19 (Friday)

Posted on by What did you learn in School today ?

Today, I learned that:

There are two blind men who go shopping, and what is the one thing that you most often have to go and buy when you go shopping when you’re a man? It’s usually socks because you put them into the wash and one of them disappears. And even though they are both blind it turns out that their wives like them to wear coloured socks and their wives like variety. So together, they go off and buy five pairs of socks each; a blue pair, a red pair, a pink pair, a green pair, and an orange pair. Now, the shop assistant finds this a somewhat eccentric purchase and gets slightly muddled and puts all ten pairs of socks into the same bag and they leave the shop, and one of them has got a bag with ten pairs of socks, the other has no socks.

Shortly before going their separate ways and going home and showing their socks proudly to their wives and saying, ‘Look what I’ve bought today,’ they realise that one of them has got all the socks. They say, my God, how can we sort out this problem so that each of us has one blue pair, one red pair, one pink pair, one green pair, and one orange pair? The question is the following: how do the two blind men achieve this goal without their wives helping them, without the socks being of different lengths, without the socks having any different texture or whatever? As far as the blind men are concerned they wouldn’t be able to tell the blue pair from the red pair. But how would they ensure that they could divide the socks up so that each of them would have two blue socks, two red socks, two pink socks, two green socks, and two orange socks ?

There is a very simple solution to the problem. I will give you time until Sunday, two whole days, to try and solve it.

Update 2016-02-21: A solution to this riddle can be found on Solution to riddle # 1 (Two blind men).

Refs.:

+: What did you learn in school today ?