X Frequency  -3 15  -1 20  0 25  1 20  2 15  Given the above frequency values for variable X, what is the expected value (mean)...

X Frequency 
-3 15 
-1 20 
0 25 
1 20 
2 15 
Given the above frequency values for variable X, what is the expected value (mean) of X? 


A professor receives, on average, 1 e-mail from students in every three hours on the day before the midterm exam. What is the probability that this professor will receive at least 6 emails on the day before the exam?