Answer:
By the Empirical Rule, 68% of light bulbs last between 1345 hours and 1455 hours
Step-by-step explanation:
The Empirical Rule states that, for a normally distributed random variable:
68% of the measures are within 1 standard deviation of the mean.
95% of the measures are within 2 standard deviation of the mean.
99.7% of the measures are within 3 standard deviations of the mean.
In this problem, we have that:
Mean = 1400 hours
Standard deviation = 55 hours
Using the empirical rule, what percentage of light bulbs last between 1345 hours and 1455 hours?
1345 = 1400 - 1*55
So 1345 is one standard deviation below the mean.
1455 = 1400 + 1*55
So 1455 is one standard deviation above the mean.
By the Empirical Rule, 68% of light bulbs last between 1345 hours and 1455 hours
