Forty nine x plus 15x -ggsg and y will get 13
A parabola is a curved shape in a graph that has either a maximum or a minimum (which is the fixed point) and any point is equidistant from that fixed point. You can tell it is a parabola because most likely in an equation the x with be squared.
In order to solve this, you have to take the number of copies of the Prisoner of Azkaban and divide it by the number of copies of the Sorcerer's Stone:
13.2÷20=0.66
To get this into a percentage, multiply the 0.66 by 100, and get 66%, meaning that The Prisoner of Azkaban was sold only 66% as much as The Sorcerer's Stone.
Following the table and knowing that the total number of students interviewed were 158 ( we can see this by looking adding either the total number of upperclassment or adding the total number of people with jobs or no jobs, this value is at the bottom right of the table in the figure attached).
Recall that:

In the figure provided each of these terms is highlighted in a different color. To convert these values to their matching probabilities we have to divide each by the total number of students, this is due to the fact that the probability is the number of favorable cases (in this case a group matching the qualities we seek) divided by the total amount of cases ( that is the total number of people interviewed). In the figure the answer is provided. For the intersection of the two events we're looking for people that is both an undercalssman and also has a job.