A company installs 5000 light bulbs, each with an average life of 500 hours, standard deviation of 100 hours, and distribution approximated by a normal curve. How many bulbs should have a life expectancy between 400 and 600 hours?

Question

kropot72 · Answer

The empirical rule for a normal distribution tells us that approximately 68% of the data points lie within the range of plus and minus one standard deviation of the mean. In this case the range plus and minus one standard deviation of the mean is between 400 and 600 hours.
Therefore the number of bulbs that should have a life expectancy between 400 and 600 hours is 68% of 5000.