Posts filed under ‘Malba Tahan’

Black Eyes and Blue Eyes

The problem, put very simply, is the following: I own five beautiful slave girls, recently purchased from a Mongol prince. Two of those young enchantress’s have black eyes; the other three, blue eyes. The two have a truthful answer to any question, whereas the three with black eyes always give a truthful answer, whereas the three with blue eyes are born liars and never answer with the truth. In a few moments the five of them will be brought here, all of their faces covered by a heavy veil, which will make it impossible for you to see their faces. You must discover, with no room for error, which of them have black eyes and which blue eyes. You may question three of the five slaves, one question to each one. From the three answers, you must solve the problem and explain the precise reasoning that led you to your answer. Your Questions should be quite simple ones, well within the compass of these slaves to answer.

From THE MAN WHO COUNTED by Malba Tahan
Chapter 33: EYE TO EYE
Download: .pdf

September 12, 2010 at 4:46 pm Leave a comment

The Lightest Pearl

A merchant of Benares, in India, had in his possession eight pearls identical in shape, size, and color. Of these eight pearls, seven were the same weight, while the eighth weighed slightly less than the others. How could the merchant discover which pearl was lighter, using a scale but making only two weighings and not using any weights?

From THE MAN WHO COUNTED by Malba Tahan
Download: .pdf

September 12, 2010 at 4:01 pm 1 comment

The Disappearing Dinar

A bill of 30 dinars is paid by the three men, each putting up 10 dinars. It turns out that there was an error; the bill was only 25 dinars. They get back 5 dinars; each takes 1 dinar, and the remaining 2 dinars are given to the slave who served them.
However, someone finds this strange, because now each has paid 9 dinars making a total of 27 dinars. Adding in the 2 dinars given to the slave only makes 29 dinars. How did 1 dinar disappear?

Mathematical excerpts from The Man Who Counted by Malba Tahan

September 12, 2010 at 3:42 pm 1 comment


Seven are the gates of hell
Seven are the days of the week
Seven wise men of Greece
Seven the seas that cover the earth
Seven the planets, and seven
The wonders of the world

From THE MAN WHO COUNTED by Malba Tahan
Download: .pdf

September 12, 2010 at 3:29 pm Leave a comment

The puzzle of the five discs

“When Princess Dahize was eighteen years and twenty-seven days old, her hand in marriage was sought by three princes whose names have passed into legend: Aradin, Benefir, and Comozan.

“King Cassim was uncertain. Of the three rich suitors, how could he choose the one who should marry his daughter? If he were to do so, it could have the following fatal result: he, the king, would gain a son-in-law, but the two unsuccessful suitors would become his bitter enemies. It was a hard decision for a sensitive and cautious king who only wanted to live in peace with his people and his neighbors. He asked Princess Dahize, but she declared only that she would marry the one who was most intelligent.

“Her decision pleased King Cassim, for he saw a simple solution to what seemed an impossible choice. He summoned five of the wisest men in his court and told them to put the three princes through a rigorous test to see which of the three was the most intelligent.

“When they had done so, the wise men reported to the king that all three princes were indeed most intelligent. They were well versed in mathematics, literature, astronomy, and physics. They could solve difficult chess problems, the subtleties of geometry, and all kinds of complex enigmas. ‘We do “not see any way,’ said the wise men; “of making” a clear decision in favor of one of them.

“After this distressing failure, the king decided to consult a dervish who had a reputation for knowing much about magic and the occult.

“The dervish addressed himself to the king. ‘I know only one way that will allow us to decide which prince is the most intelligent of the three—the test of the five disks.’

“‘Then let us do it!” exclaimed the king.

“The three princes were summoned to the palace, and the dervish, showing them five simple wooden disks, said to them, ‘Here are five disks, two of them black and three of them white. They are all the same size and weight and are different only in color.’

“Next, a page carefully bound the eyes of the three princes so that they could-see nothing. The old dervish then picked three disks at random and fastened one each to the backs of the three suitors, saying as he did so, ‘Each one of you has on his back a disk whose color you do not know. You are to be questioned in turn. The one who discovers the color of the disk he is wearing will be declared the winner and will receive the hand of the beautiful Dahize in marriage. The first one questioned can look at the disks of the other two. The second can see only the disk of the third, and the third must make his reply seeing none of the others. The one who gives the correct answer must, in order to prove that he was not simply guessing, justify his answer by clear reasoning. Now, who wants to go first?’

“‘Let me be first,’ said Prince Comozan promptly.

“The page removed the bandage from his eyes, and Prince Comozan saw the disks on the backs of his two rivals. The dervish took him aside to hear his answer, but it was wrong. Declaring himself beaten, he withdrew. He had seen the two disks on the hacks of the other princes and still not been able to determine the color of his own disk.

“‘Prince Comozan has failed,’ said the king in a loud voice, to inform the other two.

“Then let me be next,’ said Prince Benefir. Once his eyes were uncovered, the second prince saw the disk worn by the third on his back. He motioned to the dervish and whispered his reply to him. The dervish shook his head. The second prince was also mistaken and was given leave to withdraw immediately. Only one was left, Prince Aradin.

“When the kin” announced that-the second suitor had also failed, he approached with his eyes still bandaged and announced in a loud voice the correct color of the disk on his back.”

When the story was finished, the wise man pf Cordoba turned to Beremiz and said, “In making his answer. Prince Aradin reasoned in such a way as to reach with complete certainty the solution to the problem of the five disks and to win the hand of the beautiful Dahize. Now, I wish you to tell me, first, what his reply was and, second, how he could be so “sure of the color of his own disk.

The Man Who CountedA Collection of Mathematical Adventures
by Malba Tahan
Download: .pdf

August 31, 2010 at 1:31 pm Leave a comment

The Man Who Counted

The Man Who CountedA Collection of Mathematical Adventures
by Malba Tahan

August 12, 2010 at 11:55 pm Leave a comment

Circular Reasoning

Harim and Hamed each bring 30 melons to be sold in the market. Harim’s melons are to be sold at a price of 3 for 1 dinar, whereas Hamed’s are to be sold at the higher price of 2 melons for 1 dinar. The total revenue would be 10+15=25 dinars.

The seller fears that selling them as instructed will not work out, and decides to sell the 60 melons at the same time for the price of 3+2=5 melons for 1+1=2 dinars.

However, after selling all melons this way, he only made (60/5)x2=24 dinars.

How could that be?

Mathematical excerpts from The Man Who Counted by Malba Tahan

August 12, 2010 at 4:54 pm Leave a comment

Seventh Heaven

21 identical casks of wine, of which 7 full, 7 half full, and 7 empty, are to be divided among three men. Each should receive the same amount of wine and the same number of casks, without opening them.

How to do this?

Mathematical excerpts from The Man Who Counted by Malba Tahan

August 12, 2010 at 4:45 pm Leave a comment

Going to Market

A shopkeeper has lent 50 dinars to a sheik, and another 50 to a merchant. The sheik paid the debt in four installments of 20, 15, 10, and 5 dinars:

Installment Paid Still Owed
1 20 30
2 15 15
3 10 5
4 5 0
Total 50 Total 50

The merchant paid the debt in four installments of 20, 18, 3, and 9 dinars:

Installment Paid Still Owed
1 20 30
2 18 12
3 3 9
4 9 0
Total 50 Total 51

How to explain the difference of 1 dinar?

Mathematical excerpts from The Man Who Counted by Malba Tahan

August 12, 2010 at 3:38 pm Leave a comment

In So Many Words

A jeweler promised to pay old Salim 20 dinars for lodging if he sold all of his jewels for 100 dinars, and 35 if he sold them for 200. He actually sold them all for 140 dinars.

The jeweler argues that he owes old Salim 24.5 dinars: 35 dinars for lodging per 200 sales is the same as 3.5 per 20. Thus, 140 sales translates into 7×3.5=24.5 for lodging.

Old Salim wants to get 28 dinars, because 20 dinars for lodging per 100 sales is the same as 2 per 10. Thus, 140 sales translates into 14×2=28 for lodging.

How much does the jeweler owe Salim according to this agreement?

Mathematical excerpts from The Man Who Counted by Malba Tahan

August 12, 2010 at 3:15 pm Leave a comment

Older Posts