Problem 3, question "c"
Can you please specify why are we allowed to consider two bedrooms as one bedroom?
If we think about rooms as positions, they are 2 different ones. Are you sure we can reduce the initial number of positions by just 1 instead of 2?
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Since the two bedrooms will be painted in the same color, we need to choose 6 colors among all 9 options. This is equivalent to considering 6 rooms instead of 7 and reaches the same solution, namely,
Hope this helps! Let me know if something remains unclear!