The price for the stock of
Amazon.com can go either up or down during each trading day.
Itâ€™s closing price at the end of the day will be either higher or lower
than its price that closed the previous day. Consider a 5 week time period with n=25
trading days. How many combinations are there where
the stock goes up on x=20 of the days and down on the other n-x=5 days?