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First we started with February, because it is the only one with 28 days, so it is Unique. Then, we worked out January. February starts on a Saturday, so we know that January must finish on a Friday and have 31 days. We know that March is 31 days and must start on a Saturday as February finishes on a Saturday. We then repeated this process until we got to September. The only tricky moment was. There was a choice of two months that started on Monday, but the 30 day one was the correct choice.