KöMaL 2008 B4122
7 fields of a 5×5 chessboard are red, and 18 fields are blue. Two of the red fields lie along the edge of the board. Line segments separating two red fields are also coloured red, and line segments separating blue fields are coloured blue. All the rest of the lines, including the edges of the board, are black. There are 35 black line segments altogether. How many red line segments are there?
Official text KöMaL. Quoted with source.
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