Is it o.k. for a married man and a single woman to be friends?

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I asked this question earlier but i left out a few details. Suppose a married and considerably older man is friends with a younger single women. The man works out of town so the wife is not in the picture. The single woman goes to talk to the man on his job and it's a strict friendship. If they know their limits and no lines are crossed just strictly friends is there anything wrong with it?