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The average battery life of the iPhone 4S is reported to be 6

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The average battery life of the iPhone 4S is reported to be 6.0 hours by Apple. Assume that the population standard deviation for the battery life for this cell phone is 30 minutes. A random sample of 50 iPhones had an average battery life of 5.7 hours.

Determine the margin of error (in hours) for the 90% confidence interval for this sample.