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a student divides all 30 marbles into 5 boxes, paints a few marbles

Source: VMO 2021 P6 Vietnam National Olympiad

December 26, 2020
combinatoricsColoring

Problem Statement

A student divides all 3030 marbles into 55 boxes numbered 1,2,3,4,51, 2, 3, 4, 5 (after being divided, there may be a box with no marbles). a) How many ways are there to divide marbles into boxes (are two different ways if there is a box with a different number of marbles)? b) After dividing, the student paints those 3030 marbles by a number of colors (each with the same color, one color can be painted for many marbles), so that there are no 22 marbles in the same box. have the same color and from any 22 boxes it is impossible to choose 88 marbles painted in 44 colors. Prove that for every division, the student must use no less than 1010 colors to paint the marbles. c) Show a division so that with exactly 1010 colors the student can paint the marbles that satisfy the conditions in question b).