A special die has a number on each of its six faces. The sums of the numbers on opposite faces are all equal. Five of the numbers are 5, 6, 9, 11 and 14. What number is on the sixth face ?

Tom wrote all the numbers from 1 to 20 in a row and obtained the 31-digit number

1234567891011121314151617181920

Then he deleted 24 of the 31 digits, so that the remaining number was as large as possible

Which number was it .

Peter went hiking in the moutains for 5 days. He started on Monday and his last trip was on Friday. Each day he walked 2 km more than the day before. The total distance he walked during the five days was 70 km. What distance did Peter walk on Thurday ?

In a chocolate store, one chocolate costs 3 dollars. One day the store had a deal: “ Buy two and get a third one free” and Adam decided to take 49 chocolates. How much did he pay for the chocolates ?

Eight kangaroos stood in a line as shown in the diagram.

At some point, two kangaroos standing side by side and facing each other exchanged places by jumping past each other. This was repeated until no further jumps were possible.

The Modern Furniture store is selling sofas, loveseats, and chairs made from idential modular pieces as shown in the picture. Including the armrests, the width of the sofa is 220 cm and the width of the loveseat is 160 cm

What is the width of the chair ?

There are five padlocks and 5 keys-one for each of them ( see the figure ). The number code on each key has been modified into a letter code on the corresponding padlock. Equal digits have been replaced by the same letter, and different digits – by different letters. What is the number code on the fifth key ?

Boris has an amount of money and three magic wands that he can use only once. Wand A adds 1 dollar. Wand S subtracts 1 dollar. Wand D doubles the amount. In which order must he use these wands to obtain the largest amount of money ?

A vase weighs 600g when oe third of it is filled with water. The same vase weighs 800g when two thirds of it are filled with water. What is the weight of the vase when it is empty ?

Rafael has three squares. The first one has side length 2 cm. The second one has side length 4 cm and a vertex is placed in the centre of the first square. The last one has side length 6 cm and a vertex is placed in the centre of the second square, as shown in the picture. What os the area of the figure ?

The natural numbers are arranged in the form of a triangle: 1 is in the first row, 2 and 3 are in the second row, 4, 5 and 6 are in the third row, and so on. What is the sum of the numbers written in the 10^th row ?

There are eight balls numbered with the numbers 40, 80, 100, 101, 190, 200, 260 and 292 in a bag. Martina takes four balls out of the bag and calculates the sum of the numbers on these balls. It appears that this sum is half of the sum of the numbers on the balls that remain in the bag. What is the greatest number written on the balls taken out ?

The structure on the figure is made of unit cubes glued together. Morten wants to put it into a rectangular box. What are the dimensions ( length, width and height ) of the smallest box he can use ?

Four players scored goals in a handball game. All of them scored a different number of goals. One of the players, Mike, scored the least number of goals. The other three players scored 20 goals in total. What is the largest number of goals Mike could have scored ?

Ala likes even numbers, Beata likes numbers divisible by 3, Celina likes numbers divisible by 5. Each of these three girls went separately to a basket containing 8 balls with numbers written on them, and took all the balls with numbers she liked. It turned out that Ala collected balls with numbers 32 and 52, Beata – 24, 33 and 45, Celina – 20, 25 and 35. In what order did the girls approach the basket  ?