Statistics: life span of electric light bulbs; normal distribution of student scores
(1). A company manufactures electric light bulbs that have an average life of 1000 hours and a standard deviation of 50 hours. Find the probability that a bulb selected at random will have a life span of between 900 and 950 hours. (2). In an examination the mean score was 80, the standard deviation was 10, and the grades foll