Monthly rates of return on the shares of a particular common stock are independent of one another

Question:

Monthly rates of return on the shares of a particular are independent of one another and normally distributed with a standard deviation of 1.6. A sample of 12 months is taken.
a. Find the probability that the sample standard deviation is less than 2.5.
b. Find the probability that the sample standard deviation is more than 1.0. Common Stock
Common stock is an equity component that represents the worth of stock owned by the shareholders of the company. The common stock represents the par value of the shares outstanding at a balance sheet date. Public companies can trade their stocks on...