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There's an interesting trick you can do with an 11 \times 11 square...
It's possible to make five rectangles, each with different widths and lengths, using each of the following dimensions once only: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, that can be used to tile the 11 \times 11 square!
Convince yourself that only one of the arrangements below could satisfy these conditions.
Can you find the dimensions of the five rectangles which can tile the 11 \times 11 square?
Can you find all the possible different solutions?
Here different means not a reflection or rotation of another solution.
With thanks to Don Steward, whose ideas formed the basis of this problem.