Answer:
20 questions
Explanation:
1.) Use the following equation:
 =
 = 

2.) For this equation,
- x is the # of test question you got right
- y is the total # of test questions
- p is the grade you got on the test
3.) Substitute
 =
 = 

4.) Solve
 =
 = 

 =
 = 

 =
 = 

5.) Cross Multiply
 =
 = 

5x = 100
6.) Divide
5x = 100
x = 20
Therefore, you got 20 questions right.