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# How many faces have pairs of parallel lines in an heptagonal prism?

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### How many faces have pairs of parallel lines in decagonal prism?

12 faces.
The number of parallel lines will depend on whether or not the
prism is regular and right. In a regular right prism there are 10
parallel edges along the "length". 10 parallel lines make 45 pairs
(1-2, 1-3, 1-4, ... 2-3, 2-4, ... etc).
Each line at a base has one parallel line at the same base and
two at the opposite base. Each such quartet makes 6 pairs of
parallel lines and there are 5 such quartets - so 30 pairs of
parallel lines in the bases.
That makes a grand total of 75 pairs of parallel lines.