Problems

Two weighings. There are 7 coins which are identical on the surface, including 5 real ones (all of the same weight) and 2 counterfeit coins (both of the same weight, but lighter than the real ones). How can you find the 3 real coins with the help of two weighings on scales without weights?

The cells of a \(15 \times 15\) square table are painted red, blue and green. Prove that there are two lines which at least have the same number of cells of one colour.

Cutting into four parts. Cut each of the figures below into four equal parts (you can cut along the sides and diagonals of cells).

We are looking for the correct statement. In a notebook one hundred statements are written:

1) There is exactly one false statement in this notebook.

2) There are exactly two false statements in this notebook.

...

100) There are exactly one hundred false statements in this notebook.

Which of these statements is true, if it is known that only one is true?

Solve the rebus \(AC \times CC \times K = 2002\) (different letters correspond to different integers and vice versa).

Can the equality \(K \times O \times T\) = \(U \times W \times E \times H \times S \times L\) be true if instead of the letters in it we substitute integers from 1 to 9 (different letters correspond to different numbers)?

Rebus. Solve the numerical rebus \(AAAA-BBB + SS-K = 1234\) (different letters correspond to different numbers, but the same letters each time correspond to the same numbers)

Multiplication of numbers. Restore the following example of the multiplication of natural numbers if it is known that the sum of the digits of both factors is the same.

Restore the example of the multiplication.

Prove that the number of all arrangements of the largest possible amount of peaceful bishops (figures that move on diagonals and don’t threaten each other) on the \(8\times 8\) chessboard is an exact square.