The Eurostar was Europe’s first international train, designed to take advantage of the Channel Tunnel that connects England with Continental Europe. It carries nearly 800 passengers and occasionally reaches a peak speed of more than 190 mph

(http://www.o-keating.com/hsr/eurostar.htm). Assume the standard deviation of train speed is 19 mph in the course of all the journeys back and forth and that the train’s speed is normally distributed.

Suppose speed readings are made during the next 20 trips of the Eurostar and the mean speed of these measurements is 184 mph.

a. What is the variable being studied?

b. Find the 90% confidence interval estimate for the mean speed.

c. Find the 95% confidence interval estimate for the mean speed.