The life in hours of a 100-watt bulb is known to be approximately normally distr

Question

The life in hours of a 100-watt bulb is known to be approximately normally distributed. A random sample of 20 bulbs has a mean life of 2050 hours standard deviation of 12.5 hours. Construct a 95% two-sided confidence interval on the mean life. Also, Suppose we want the total width of the confidence interval on mean life to be five hours. What sample size should be used: if the desired confidence level is 95%? Note that the half-width of the confidence interval is equal to maximum error in estimation.

Explanation / Answer

Try this website: http://www.dimensionresearch.com/resources/calculators/sample_size.html.It helped me.

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