A random sample of 118 lightning flashes in a certain region resulted in a sampl

Question

A random sample of 118 lightning flashes in a certain region resulted in a sample average radar echo duration of 0.86 sec and a sample standard deviation of 0.43 sec. Calculate a 99% (two-sided) confidence interval for the true average echo duration . (Round your answers to two decimal places.)

  ,

sec

Interpret the resulting interval.

A. We are 99% confident that the true population mean lies below this interval.

B. We are 99% confident that this interval does not contain the true population mean.    

C. We are 99% confident that this interval contains the true population mean

D. We are 99% confident that the true population mean lies above this interval.

Explanation / Answer

mean is 0.86 and s is 0.43

for sample size of 118, the standard error SE=s/sqrt(N)= 0.43/sqrt(118)=0.03958

for 99% confidence the z value is 2.576

thus the lower bound is mean-z*SE= 0.86-2.576*0.03958=0.7580

the upper bound is mean+z*SE= 0.86+2.576*0.03958=0.96196

answer is C

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