Example 1 is easy - 400 shares ....
Good stuff - thank you. I guess I always imagined it more like betting at a track, where there was someone/something (i.e. an algorithm) behind the scenes "setting" the price to try to accommodate/encourage trades to occur, in the same way an oddsmaker tries to set the odds to encourage betting. Seems more like the role of the market managers is really just to record the stock prices of the trades that the traders mutually agree upon among themselves.