7(b)

(7) The life of a television tube measured in hours of use, is normally distributed with a mean of 5000 hours and a standard deviation of 1000 hours. (3) Find the probability that a TV tube will last for (i) between 5500 and 6500 hows, (ii) less than the expected life of a tube. (b) Find the probability that for someone using a TV for 1500 hours per year, the tube will last for less than 5 years