Jason is a high school basketball player. In a particular game, he made some free throws (worth one point each) and some two point shots. Jason made a total of 13 shots altogether and scored a total of 20 points. Write a system of equations that could be used to determine the number of free throws Jason made and the number of two point shots he made. Define the variables that you use to write the system.

Let x represent the number of free throws Jason made and y represent the number of two point shots he made.

The system of equations is:

1. x + y = 13 (since Jason made a total of 13 shots)
2. x + 2y = 20 (since each free throw is worth 1 point and each two point shot is worth 2 points, and Jason scored a total of 20 points)

Therefore, the system of equations is:
x + y = 13
x + 2y = 20