Answer:
Desiree answered 40 questions correctly
Explanation:
Let
x = number of questions answered correctly
y = number of questions unanswered
z = number of wrong answers unanswered
The system of equations can be expressed
x + y + z = 50
3*x - 0.5*y -1*z = 110
Desiree did not leave any question unanswered
This means that the equations become
y = 0
x + z = 50
3*x -z = 110
If we add them together, we get
4x = 160
x = 40
z = 10
She answered 40 questions correctly