IMAS 2011 — Upper Primary Grades 5–6 — Round 2 Question 13

As shown in the diagram, there are five pieces used in the video game Tetris. We have four identical copies of each piece. From the twenty copies, we choose four and try to use them to form a $ 4 \times 4 $ square. The copies may be turned or flipped. How many different choices are there?

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**(e)**