To perform last week's trick, the math magician just has to choose his own secret number and mentally do the same as he has asked his audience.
Our regular commentator Manuel Amorós has verified it:
“I've done the Kruskal counting card trick several times and it often impresses the staff.
It is based on the fact that, whatever the number initially chosen, if the described process is followed, it will eventually end up in a certain letter (or a word if we use a text).
To perform the trick, therefore, the magician just needs to mentally choose a number and follow a process parallel to that of the volunteer, having the almost complete certainty that it will converge with it after a certain time.
This means that he has to extend the game as long as possible and wait for the end of the deck of cards to announce the secret number of the volunteer.
And in relation to the Kruskal brothers, Francisco Montesinos provides the following information:
“William was not one-armed either.
Together with Wallis, he was the creator of the so-called Kruskal-Wallis test, widely used in non-parametric statistics ―which is used when the parameters of the population from which a sample has been extracted are unknown— to determine if In view of them, it can be argued that the data available belong or not to a single population.
Count sheep to not fall asleep
If we go from card counting to sheep counting (not to fall asleep, but quite the opposite: to keep our neurons wide awake), we find ourselves with a rich vein of mathematical puzzles from oral culture.
Which is not surprising when we consider that, just as geometry was promoted by agriculture, surely arithmetic developed from livestock.
Hunter-gatherers would not care if there were 13 or 14 units in a handful of berries, but a sheep more or less at the time of putting them into the fold was a piece of information of the greatest importance.
So let's look at three problems related to counting sheep, one very easy, one not so easy, and one difficult.
The very easy one is a classic that I usually use to explain first-degree systems of equations to children:
"Give me one of your sheep and then I will have twice as many as you," says one shepherd to another.
"Give me one and so we'll both have the same number," replies the second.
How many sheep does each have?
In the not-so-easy one, that prodigious calculator intervenes, who with a simple glance could determine how many sheep there were in a flock, and who explained his ability by saying that he counted the legs and divided them by 4. Well, our leg counter sees a flock and tells the shepherd:
—You have a lame sheep, I have counted 59 legs.
"I have several cripples, although most of them are fine," answers the pastor.
How many whole sheep and how many lame are in the flock?
And the difficult one I have taken from a book by the prolific French novelist, essayist and engineer Jean-Pierre Alem:
Two brothers sell a herd of sheep and collect a certain number of 10-euro bills, plus a peak, in 1-euro coins, less than 10 euros.
Each sheep is worth as many euros as there are sheep.
The brothers share the money in the following way: the oldest takes a 10 bill, the youngest takes another, and so on until the oldest takes the last bill and the youngest takes the peak.
And since the younger brother has earned a little less in this way, the older brother takes one euro coins out of his pocket and gives them to him, so that both parties are equal.
How many coins has the older brother taken out of his pocket?
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