Question 5: The local authorities in a certain city install 10000 electric lamps in streets of the city. If these lamps have an average life of 1000 burning hours with a standard deviation of 200 hours, assuming normality, what number of lamps might be expected to fail (i) in the first 800 burning hours?; (ii) between 800 and 1200 burning hours? After what period of burning hours would you expect that (a) 10% of the lamps would fail?; (b) 10% of the lamps would be still burning?