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September 1, 2014

Homework Help: Math

Posted by alice on Wednesday, December 5, 2012 at 1:36pm.

What is the approximate percentile rank of a lightbulb that failed at 9000 hours if the number of lightbulbs is 400? The number of lightbulbs that lasted between 5400 and 9000 were about 326 lightbulbs. The mean is 7800 and the standard deviation is 1200

My guess was: percentile = 9000 hours/400 lightbulbs = 22.5, but I'm not sure if I'm solving this right

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