Let n represent students and m represent non-students.
The total number who attended was 1100. Meaning if we add both the students and non students, we should be 1100.

The paid a gate fee of $2 while non students paid $3 and the total was $2800

We now solve the two equations simultaneously.
Let us make m the subject in equation (1) to get

Now, let us put (3) in equation (2) to obtain,

We expand solve for m.


Simplify to obtain,

Divide through by -1

Substitute this value into equation (3)
to obtain,

Therefore 600 were sold to non students while 500 were sold to students.
In other word 500 pieces of the $2 and 600 pieces of $3 were sold.