50 question multiple choices with A, B, C, D
Probability of an unsual score?
Probability of between 20 and 30 correct inclusive?
I assume you want the probability of getting 20 to 30 right by random guessing of answers. The mean value will be 1/4 x 50 = 12.5 and the standard deviation will be sqrt (.25*.75*50) = 3.1
Using the normal distribution Java tool at this website,
http://psych.colorado.edu/%7Emcclella/java/normal/accurateNormal.html ,
I get the probability of 20 to 30 correct answers to be 0.78%