Empirical research on stock market data indicates that over the course of a year, 50% of stocks go up. A random sample of 400 stocks is going to be chosen at the beginning of next year. Let p be the proportion of the stocks in the sample that go up over the course of a year. Answer the following. (If necessary, consult a list of formulas.) (a) Find the mean of p. X 5 ? (b) Find the standard deviation of p (c) Compute an approximation for P (p