<PRE><B>Question 1180017</B>
mean is 7000 hours.
standard deviation is 796 hours.
z-score = (x - m) / x
x is the raw score = 8500
m is the mean = 7000
s is the standard deviation = 796  hours
z-score = (8500 - 7000) / 796 = 1.884422111.
area to the left of that z-score is .9702461149
area to the right = 1 minus that = .0297538851.
the percentage of light bulbs that can be expected to last more than 8400 is .0298 rounded to 4 decimal places = 2.98% rounded to 2 decimal places.
you can use the following calculator to get the same answer.
&lt;a href = &quot;https://www.gigacalculator.com/calculators/z-score-calculator.php&quot; target = &quot;_blank&quot;&gt;https://www.gigacalculator.com/calculators/z-score-calculator.php&lt;/a&gt;
let me know if you have any trouble getting the same results.




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