Question

A simple random sample of 12 e-readers of a certain type had the following minutes of battery life.

287, 311, 262, 392, 313, 281, 274, 316, 286, 265, 322, 291

Assume that it is reasonable to believe that the population is approximately normal and the population standard deviation is 57. What is the upper bound of the 95% confidence interval for the battery life for all e-readers of this type?

Round your answer to one decimal places (for example: 319.4). Write only a number as your answer. Do not write any units.

Answer 1

We have for given sample,          
              
Sample mean =300      
Population standard deviation=57  
Sample size=12      
Level of significance =0.05      
Z critical value (by using Z table)=1.96      
              
Confidence interval upper limit formula,
          


=332.3

Upper confidence limit =332.3