There are 40 students in an elementary statistics class. on the basis of years of experience, the instructor knows that the time needed to grade a randomly chosen first examination paper is a random variable with an expected value of 6 min and a standard deviation of 6 min. if a grading times are independent and the instructor begins grading at 6: 50 p. m. and grades continuously, the (approximate probability that he is through grading before the 11: 00 p. m. tv news begins is probability isif the sports report begins at 11: 10 p. m., the probability that he misses part of the report if he waits until grading is done before turning on the tv is