90. The article “A Probabilistic Model of Fracture in Concrete and Size Effects on Fracture Toughness” (Magazine of Concrete Res., 1996: 311–320) gives arguments for why the distribution of fracture toughness in concrete specimens should have a Weibull distribution and presents several histograms of data that appear well fit by superimposed Weibull curves.

Consider the following sample of size n
18 observations on toughness for high-strength concrete (consistent with one of the histograms); values of pi
(i  .5)/18 are also given.

Observation .47 .58 .65 .69 .72 .74 pi .0278 .0833 .1389 .1944 .2500 .3056 Observation .77 .79 .80 .81 .82 .84 pi .3611 .4167 .4722 .5278 .5833 .6389 Observation .86 .89 .91 .95 1.01 1.04 pi .6944 .7500 .8056 .8611 .9167 .9722 Construct a Weibull probability plot and comment.