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MathNet 2021 — Part 09 Question 65

Math Olympiad Vault · MathNet 2021 — Part 09

Question 65

A student divides $30$ marbles into $5$ boxes labelled $1, 2, 3, 4, 5$ (there may be a box without marble).

Part (a). How many ways are there to divide marbles into boxes (two ways are different if there is a box with different number of marbles)?

Part (b). After dividing, this student paints those marbles by a number of colors (each marble have one color, one color can be painted for many marbles), such that there does not exist $2$ marbles in the same box, having a mutual color and from any $2$ boxes, it is impossible to choose $8$ marbles painted in $4$ colors. Prove that for every division, the student must use at least $10$ colors to paint the marbles.

Part (c). Find a division so that the student can use exactly $10$ colors to paint the marbles that satisfies the conditions in question b).