posted by chris .
In a transportation study of 20 large cities, it was found that the mean of the number of cars per person was 0.504. (Some of the people in the city are children.) The study also stated that the standard deviation s was 0.123. Find a 95 % confidence interval for the true mean number of cars per person.
I think I know the formula 99%=0.504 + 1.96 SEm but is the SEm 1.96?
SEm = SD/√n