A researcher wishes to find out if the published max speed of a 737 jet is accurate, but needs to know how many jets to include in the sample. From past studies it is.
known that the population standard deviation of speeds is 68 mph.
(a) Assuming that she would like to be 90% confident of the results, indicate the
critical value that corresponds to this given level of confidence. Round to two
decimals and remember that critical values are defined to be positive.
(b) If she would like to have a maximum error of 15 mph, how many jets should be
sampled?