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## 'Red Even' printed from http://nrich.maths.org/

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(a) You have 4 red and 5 blue counters. How many ways can they
be placed on a 3 by 3 grid so that all the rows columns and
diagonals have an even number of red counters?

(b) It is now only required that all the rows and columns have
an even number of red counters. Are there any additional solutions?
Two solutions are considered the same if one can be transformed to
the other by rotating the square.