Since getting four questions wrong out of 20 means getting 80 percent correct, it corresponds to a B letter grade in most cases. However, depending on the grading scale and whether curved grading is employed, the letter grade can vary.
For example, many teachers use a plus-or-minus grading system, where an 80 percent corresponds to a B- letter grade, and an overall score of 80 percent in a course corresponds to 2.75 grade points. Additionally, some teachers may use entirely different cutoffs for assigning letter grades. Some teachers grade tests on a curve when they find that a test is too difficult for the class and allot points to every student's final grade to adjust the class average as necessary. Most professors at the college level include information about their grading systems in the syllabus for each course.