64. The accompanying frequency distribution of fracture strength (MPa) observations for ceramic bars red in a particular kiln appeared in the article Evaluating Tunnel Kiln Performance (Amer. Ceramic Soc.

Bull., Aug. 1997: 59—63).

Class 81—83 83—85 85—87 87—89 89—91 Freq. 6 7 17 30 43 Class 91—93 93—95 95—97 97—99 Freq. 28 22 13 3

a. Construct a histogram based on relative frequencies, and comment on any interesting features.

b. What proportion of the strength observations are at least 85? Less than 95?

c. Roughly what proportion of the observations are less than 90?