When data are summarized in a frequency distribution, the median can be found by first identifying the median class, which is the class that contains the median. We then assume that the values in that class are evenly distributed and we interpolate. Letting n denote the sum of all class frequencies, and letting m denote the sum of the class frequencies that precede the median class, the median can be estimated as shown below.

Use this procedure to find the median of the frequency distribution given in Table 3-2 on page 88. How far is that result from the median found from the original list of McDonald’s lunch service times listed in Data Set 25 “Fast Food” in Appendix B?

Data Set 25: Fast Food 

Data are from 400 observations (first five rows shown here) of drivethru service times (sec) at different fast-food restaurants. Times begin when a vehicle stops at the order window and end when the vehicle leaves the pickup window. Lunch times were measured between 11:00 AM and 2:00 PM, and dinner times were measured between 4:00 PM and 7:00 PM. Data collected by the author.