1.It is found that the lifetimes of television tubes manufactured by a company have a normal distribution with mean of 2000 hours and standard deviation of 60 hours. if 10 tubes are selected at random,find the probability that the sample standard deviation will a) not exceed 50 hours, b) lie between 50 and 70 hours.
2.Suppose that the acceleration of the train during the interval time from t=2 to t=4 s is a 2t m/s^2, and at t = 2 s its velocity is v = 180 km/hr. What is the train's velocity at t = 4 s, and what is its displacement (change in position) from t = 2 s to t = 4 s?