Decision tree involving probability

    Due to budget cuts a manager was told to cut a single person out of his work crew of 4 workers-Dave Joe Mike and Roger. He decided to make the cut in as fair of way as possible since all are equally qualified. He put each of their names on a card mixed the cards and drew a random name. The managers best friend is Dave and Dave stated that at least his odds of losing his job are only one out of four-it could be worse Dave stated. Then Dave asked At least two of the others-Joe Mike and Roger will retain their job; could you tell me randomly the names of the two that will keep their jobs? The manager decided to tell Dave which of the others would keep their jobs the manager stated Mike and Roger will keep their jobs..Daves concern set in he said it seems as if my chances of being terminated just went from to ..
    Is John right in thinking that the probability changed from to ? Explain/prove your answer with a decision tree only..

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