The increase or decrease in the price of a stock between the

The increase or decrease in the price of a stock between the beginning and the end of a trading day is assumed to be an equally likely random event. What is the probability that a stock will show a decrease in its closing price on 11 consecutive days.

Solution

probability that a stock will show a decrease = 0.5 (since equally likely)

probability that a stock will show a decrease in its closing price on nine consecutive days = 0.5^9 = 0.00195