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A square piece of paper is cut into 6 pieces, each of which is a convex polygon. 5 of the pieces are lost, leaving only one piece in the form of a regular octagon (see the drawing). Is it possible to reconstruct the original square using just this information?

Decipher the puzzle: \(KIS + KSI = ISK\). The same letters correspond to the same numbers, different letters correspond to different numbers.

Ten people wanted to found a club. To do this, they need to collect a certain amount of entrance fees. If the organizers were five people more, then each of them would have to pay £100 less. How much money did each one pay?

Two tribes live on the island: natives and newcomers. It is known that the natives always tell the truth and the newcomers always lie. A traveler hired an indigenous islander as a guide. On the way, they met a man. The traveler asked the guide to find out which tribe this person belongs to. The guide returned and said that the man said that he was a native. Who was the guide – a native or a newcomer?

At the cat show, 10 male cats and 19 female cats sit in a row where next to each female cat sits a fatter male cat. Prove that next to each male cat is a female cat, which is thinner than it.

Among 40 containers there are two containers of different shapes and two containers of different colors. Prove that among them there are two containers that are both of different shapes and colors.

The vendor has a cup weighing scales with unequal shoulders and weights. First he weighs the goods on one cup, then on the other, and takes the average weight. Does he deceive customers?