More probability from Frederick Mosteller:

Marvin gets off work at random times between 3 and 5 P.M. His mother lives uptown, his girlfriend downtown. He takes the first subway that comes in either direction and eats dinner with the one he is first delivered to. His mother complains that he never comes to see her, but he says she has a 50-50 chance. He has had dinner with her twice in the last 20 working days. Explain.

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this one i dont know haha.my guess is that each time whether he takes the train uptown or downtown is independent of each other?

I slept on it and when I woke up the answer came to me in the form of a dream. hahaha i’ll post the answer in a few days time – meanwhile let’s wait for replies!

hee can you give me the answer now?(; haha after your finish your 3 tests first!