There are 46 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 5 min and a standard deviation of 4 min. (Round your answers to four decimal places.) LA USE SALT (a) If grading times are independent and the instructor begins grading at 6:50 PM. and grades continuously, what is the (approximate) probability that he is through grading before the 11:00 PM. TV news begins? (b) If the sports report begins at 11:10, what is the probability that he misses part of the report if he waits until grading is done before turning on the TV? You may need to use the appropriate table in the Appendix of Tables to answer this question. Need Help? Read It Watch ItRockwell hardness of pins of a certain type is known to have a mean value of 50 and a standard deviation of 1.5. (Round your answers to four decimal places.) LA USE SALT (a) If the distribution is normal, what is the probability that the sample mean hardness for a random sample of 17 pins is at least 51? (b) What is the (approximate) probability that the sample mean hardness for a random sample of 39 pins is at least 51? You may need to use the appropriate table in the Appendix of Tables to answer this question. Need Help? Read It