Question

Come up with your own Confidence Interval problem. Feel free to use hypothetical data. Think about something that might be useful in your career or in business in general. Try to steer away from examples already used in the book. Run the problem in Megastat and explain the results.  

Answer 1

Question :

A factory produces steel rods

average length of a steel rod = 165 feet

SD (standard deviation) = 67 feet

find the 95% confidence interval of the length of rods in a random sample of 36 rods

Solution :

Confidence interval = [ mean - z*SD/(n^0.5) , mean + z*SD/(n^0.5) ]

given :

n = 36

mean = 165 feet

SD = 67 feet

and,

Z for 95% CI = 1.96

therefore 95% Confidence interval :

[ 165 - 1.96*67/(36^0.5) , 165 + 1.96*67/(36^0.5) ]

[ 143.11 feet , 186.89 feet ]

from the results we can interpret that 95% of the population will have heights between 143.11 and 186.89 feet

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