The following data represents (in thousands) the total private and public enrollment levels in grades 9 to 12 in the united staes in october 2005.
x(grade level) frequency
9 4306
10 4421
11 4490
12 4137
Construct a discrete probabilty distribution for the random variable X (hint: probability equals frequency divided by total observations) and compute the mean and standard deviation of X. (rond to 2 decimal places)