Deserved and undeserved test results

  Completely unprepared student has a statistical chance of randomly choosing the correct answer. For example, if a monkey guesses the right answers, it too will "earn" a certain number of points. This number is usually called monkey score, undeserved or random score. In a true/false question monkey score is as high as 50%. This, of course, narrows down the range of points, which makes a test as a measuring instrument less precise.
  If a test consists of multiple distracter questions, the random score decreases. If all the results are randomly guessed, the result will equal the product of the number of questions and ratio of all the correct answers and all the offered answers. 
  Students are usually sure about the correct answers to some multiple choice questions, which means than the total of all points will be:

Total number of points = number of deserved points + number of points for randomly guessed answers

  The number of randomly guessed answers for the questions a student does not know the answer to does not have to be purely coincidental. Even if a student does not know the answer to one part of the question, they can rule out some distracters (partial knowledge), and by doing so narrow down the choice. Therefore, students will answer such questions better than monkey score. If they don't know any part of the answer to the other questions, their choice of answer will be purely coincidental and therefore equal the monkey score.