William, Oliver, and James were playing snowballs. The first snowball was thrown by Oliver. Then for every snowball that hit him, William threw six snowballs, James threw five, and Oliver threw four. After a while, the game was over. Find out how many snowballs were hit if 13 snowballs flew past the target. (You do not throw snowballs at yourself.)

📜 Leaflet #equation

James said on November 28: "Today the difference between the number of full months I have lived and the number of full years I have lived is 144 for the first time. When is James' birthday?

📜 Leaflet #equation

The figure shows the unfolding of the cube. There are only numbers on it: 1 and 2. Arrange the remaining numbers: 3, 4, 5, 6 — so that the sum of the numbers on any two opposite sides is equal to 7.

📜 Leaflet #geometry

Put 9 points on the plane so that no 4 lie on the same straight line, but out of any 6 there are 3 lying on the same straight line. (In the drawing, draw all the lines on which the three marked points lie.)

📜 Leaflet #geometry

A 2×6 rectangle is marked on the checkered paper.
Is it possible to color the nodes of the cells lying on the border and inside this rectangle (there are 21 of them in total) in two colors so that no four one-color nodes appear at the vertices of the rectangle with sides running along the grid lines?

📜 Leaflet #geometry

There are several natural numbers written in a circle, each of which is not greater than one of its neighbors. Prove that among these numbers there are at least two equal ones.

📜 Leaflet #extreme

There are several numbers written in a circle, each number is equal to the arithmetic mean of two neighboring numbers. Prove that all these numbers are equal.

📜 Leaflet #extreme

Eight mushroom pickers collected 37 mushrooms. It is known that no two of them collected mushrooms equally and each found at least one mushroom. Prove that some two of them collected more than some five.

📜 Leaflet #extreme

There are several cities in the country. A crazy traveler goes from city A to the farthest city B. Then he goes to the farthest from B city C, and so on. Prove that if city C is not the same as city A, then the traveler will never go back to city A.

📜 Leaflet #extreme

There are 2023 asteroids flying in outer space, each of which has an astronomer sitting on it. All distances between asteroids are different. Every astronomer watches the nearest asteroid. Prove that no one is watching one of the asteroids.

📜 Leaflet #extreme

James conceived four non-negative numbers and counted all their possible pairwise sums (6 total). What numbers did he conceive if these sums are 1, 2, 3, 4, 5, 6?

📜 Leaflet #extreme

In a 7×7 square, paint some cells so that there are exactly 3 painted cells in each row and each column.

📜 Leaflet #coloring

Merry Christmas!