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 minutes, and a standard deviation of  6 minutes.

If grading times are independent and the instructor begins grading at 6:50 PM, and the sports report begins at 11:10 PM, what is the probability that he misses part of the report if he waits until grading is done before turning on the TV?

So  P(T_{0} > 260) = 1 - P(T_{0} \leq 260) = 1 - P \left(\frac{260-240}{37.94} \leq z \right) = 1 - \Phi(0.527) = 0.3015

Is this correct?