# SOLUTION: A random sample of 50 calls initiated on cellular car phones had a mean duration of 3.5 minutes with standard deviation 1.2 minutes. Find 99% confidence interval for the mean dura

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 Question 610782: A random sample of 50 calls initiated on cellular car phones had a mean duration of 3.5 minutes with standard deviation 1.2 minutes. Find 99% confidence interval for the mean duration of telephone calls initiated on a cellular car phone.Answer by ewatrrr(10682)   (Show Source): You can put this solution on YOUR website! ``` Hi, 50 calls initiated on cellular car phones with mean duration of 3.5 minutes & SD = 1.2 minutes Find 99% confidence interval for the mean duration of telephone calls initiated on a cellular car phone. ME = = .437 CI: 3.5-.437> u < 3.5+.437 CI: 3.063 > u < 3.947 Note: ------------------------------------------------------------- a a/2 crtical regions 80% 0.2 10% z <-1.28155 z >+1.28155 90% 0.1 5% z <-1.645 z >+1.645 92% 0.8 4% z <-1.751 z >+1.751 95% 0.05 2.50% z <-1.96 z >+1.96 98% 0.02 1% z <-2.33 z >+2.33 99% 0.01 0.50% z<-2.576 z >+2.576 ```