The manager of Cardinal Electrics light bulb division must estimate the average number of hours that a light bulb made by each light bulb machine will last. A sample of 40 light bulbs was selected from machine A and the average burning time was 1,416 hours. The standard deviation of burning time is known to be 30 hours.

1. Compute the standard error of the mean.
2. Construct a 90 percent confi dence interval for the true population mean.

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