Frequency distributions are given for the weights of cars, trucks, and light duty vehicles sold in the United States in 1975 and in 1990. The class intervals are not the same through the entire listing, however. This creates problems in plot- ting frequency polygons. These will be a correct interpretation only if the frequen- cies are converted to frequency densities by dividing the frequencies by the size of the class intervals over which they are spread. The cumulative frequency dis- trubition (plot of cumulative frequencies versus the upper class limits) interpre- tation is not affected by the non-uniform class intervals. If the frequencies are converted to relative frequencies, or probabilities, the cumulative form for a pop- ulation will be the cumulative probability distribution. The median of the population can be approximated by noting the X-value at which the graph of cumulative pro- bability crosses the 0.50 probability level. Students will want to do graphic displays permitting comparison of the distribution of weights in 1990 with those in 1975 for cars, trucks, and/or light duty vehicles.