Question 51701
a) Mean is the average of all the numbers.  You get this by adding all the populations together, and then dividing that number by the amount of cities. 
I will just ignore the fact that some of the population numbers are negative, and that you cannot have a negative population.
So the mean for your problem would be 1,164.
c) To find the standard deviation, you find the mean of the data. Substract the mean from each value and square before adding all, divide by the number of data and then find the square root.
d) The median is when you put all of the numbers in order, it is the center number.  The median in your problem is 775.