Draw a rectangular prism with a square base such that the pyramid’s vertex lies on a line perpendicular to the base of the prism
through one of the four vertices of the square base, and the distance from the vertex to the base plane is equal to the side length of the square base.
1 answer:
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Firstly, we'll fix the postions where the women will be. We have
forms to do that. So, we'll obtain a row like:
The n+1 spaces represented by the underline positions will receive the men of the row. Then,
Since there is no women sitting together, we must write that . It guarantees that there is at least one man between two consecutive women. We'll do some substitutions:
The equation (i) can be rewritten as:
We obtained a linear problem of non-negative integer solutions in (ii). The number of solutions to this type of problem are known:
[I can write the proof if you want]
Now, we just have to calculate the number of forms to permute the men that are dispposed in the row:
Multiplying all results: