Not exactly. There is no target average. However, each exam has a certain number of questions that students usually have trouble with. The number of such "hard" questions is subtracted from the total number of questions on the exam to get the effective number of questions. To calculate your score, I divide the number you got right by the effective number of questions. If that gives you a score over 100%, I drop it to 100%.

The "hard" questions are usually good questions, so I want to give credit to those who got them right. I do not let your exam score go over 100%, so you do not get "extra credit." However, getting a "hard" question right means that you can miss one of the other questions without penalty.