The lifetime distribution of a sample of 500 MRI machines across Jamaica is bell-shaped with a mean of 1500 hrs and a standard deviation of 80 hrs. At least, what percentage of these machines must have lasted (before breaking down) between 1300 and 1700 hrs? (2 mks) If the relative frequency curve for the failure times has a bell-shape,appropriately how many of these machines must have lasted between 1340 and 1580 hours? (3 mrks)