Information reference tables the lifespan of a 60-watt lightbulb produced by a company is normally distributed with a mean of 1450 hours and a standard deviation of 8.5 hours. if a 60-watt lightbulb produced by this company is selected at random, what is the probability that its lifespan will be between 1440 and 1465 hours

First, we need to standardize the value 1440 and 1465 to be able to work out the z-score







The z-scores are shown in the diagram below

To work out the probability of  we can first read on the table, the probability when , then we subtract this value from 1, as we are interested in the area to the right of 1.77.



Then the area between  and  is  which is also the probability of lifespan between 1440 and 1465