IOM 2018, Блиц, английски — Задача 21

OLYMPIAD OF METROPOLISES. Moscow, September 3 · 3 септември 2018 г.

Условие

There is an unlimited supply of chips of three colours: red, green and blue. Find the number of ways to arrange 9 chips in a circle such that each colour is present. Arrangements are considered identical if and only if they can be obtained from each other by a rotation.

Отговори

Решение

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Оригинал в Архива: blitz.pdf · официални решения: blitz-answers.pdf