We have three identical buckets filled with water to the brim. In one of them we introduce a piece of wood of half a kilo that dislodges a part of water and is floating and in another we introduce a plastic ball that weighs a quarter of a kilo that also dislodges some water and is floating. If we weigh them on a scale, which cube will weigh more?

In this peaceful place where seagulls rest on the ice and whales are seen in the distance, there are more animals than it seems. Can you find them? Solution In the mountains of ice a person hides with the dogs that pull their sled and in the center of the image a polar bear looks at the lying scene.

Maria has two boyfriends, Juan and José. To visit Juan, you must take the train northbound and to visit José you must take the train southbound. Both trains pass every 10 minutes and as Maria likes both boys equally, it is not fixed if a train goes north or south and goes up to the first one that passes.

It is known that El Greco was reputed to paint the elongated figures. King Felipe II, knowledgeable about this problem but a great admirer of the great artist's painting, put all his philosophers to think of a way for El Greco to paint a portrait of his person with the right proportions. How did the king manage to have a portrait provided?

The three different symbols in the table represent three different numbers between 1 and 9. If you add the rows and columns, you should get the results indicated outside the table. What value does each symbol have? Solution Since two spiders plus one eye add 9, the spiders can add between 1 and 4 and the eye must be odd to reach 9.

In a famous television contest the participant is required to choose a door between three (all closed) and his prize is to take away what is behind the chosen door. It is known that one of them hides a car and that after the other two there are goats. Once the contestant has chosen a door and communicates their choice, Monty, the presenter, opens one of the other doors and shows that behind it there is a goat.

In the Middle Ages, a spy from the court of King Arthur had the mission of entering a castle to investigate the plans of the enemies but upon arrival he discovered that the doors of the castle were closed and that an armed watchman controlled everyone who He was approaching so he hid among some bushes to watch.

A mathematician wrote the following in his will: My wife will receive a third of the inheritance, my son a fifth, my oldest daughter a sixth and my little daughter € 9,000. Who will receive more money from the inheritance? Solution If we call the total inheritance X, we can deduce the following equation: From here we get that x = 30.

In a basket we have 20 balls numbered from 1 to 20. How many balls must be extracted at least (without looking) to be completely sure that the sum of the numbers of the balls extracted is greater than or equal to 70? Solution The worst possible scenario would be to extract the balls with the lowest score.

To assemble my model of a sailboat I need some raft wood slats. In the modeling shop they sell them in boxes of a dozen and also in loose units although they are somewhat more expensive. So I ordered several boxes and some loose units to complete exactly what I needed.

Newton's method of finding the roots of an equation creates fractals if the variable in the equation is a complex number. Solution Jos Leys has found a way to show these fractals in 3D.

Look at this image of a door to which a part has been hidden. Do you think both sides coincide at the top? Solution Although it may not seem so if we uncover the door completely we see that both sides fit perfectly. Poggendorff's illusion is based on the optical effect that occurs when an inclined line is interrupted in a segment of a certain length that produces the effect that the resulting pieces do not belong to the same line.

An intermediary buys fruit from farmers and then sells it to market stalls. He receives the orders of the merchants and looks for the farmer to sell it to him so that he earns 4% of the total value of each transaction. Charges 2% commission to the farmer and another 2% to the merchant. However, he realized that there was the possibility of improving the benefit by trickling the scales of his balance in such a way that there was a difference of 100g for every real kilo in the weighing.

When I am about to arrive at the bus stop I realize that I forgot the clock at home, so I decide to ask the time of a lady who was passing by my side and who answers the following: From this moment, the The hour hand will take just twice as long as the minute hand to reach six.

Here is a nice problem that occurred to me during a trip from Bixley to Quixley that I did on the back of a mule. I asked Don Pedro, the native guide who walked in front of me, taking my mule from the reins, if my ride could move on to another step. He said yes, but it was much slower, so I continued my journey at a uniform speed.

In a barbecue two long tables have been prepared so that the guests sit down to eat. The following soft drinks have been purchased to distribute: 4 bottles of 1 liter. 5 bottles of 3/4 liter. 6 bottles of 1/2 liter. 5 1/4 liter bottles. We have to distribute the soda bottles between the two tables, so that each one corresponds to the same amount.

30 prisoners are informed that they are going to be placed in a row and they are going to put a hat on the head of each one, white or black, without specifying how many caps they will wear in each color. Each prisoner will only see the hats of the prisoners in front of him but not his or the ones behind.

A 100 meter long rope is nailed at both ends at the top of two posts. The posts are nailed to the ground and have a height above the ground of 90m and 70m respectively and are perpendicular to the ground. In addition, we know that the lowest point of the rope is 30m from the ground.

In the basement of a house there are four incandescent bulbs and on the top floor there are four switches, one for each bulb. When we operate a switch from the house, it is impossible to see which bulb has been lit. The question is: Making a single trip, how can we know which switch turns on each light?