Homework 23. Due Wednesday, Apr.30, 2008.
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[Although our class is cancelled, please hand this 
in by the end of the day so that I can get it to 
the Grader: our next HW will be due Friday May 2.]

Access the data "geyser" included as part of the R library MASS. 
It is a data-frame with two components, "waiting" (the 299 times 
in minutes between successive eruptions of the Old Faithful geyser
in Yellowstone park) and "duration" (the eruption times, also in
minutes).

(i) Create a scaled relative-frequency histogram for the
geyser$waiting  dataset. Over-plot two kernel density estimators,
with your choice of probability density as kernel: one with
bandwidth = 0.5, and one with bandwidth b=3.

(ii) Fit a mixture of log-normal densities, with 2 or 3 components,
to the geyser$waiting values by maximum likelihood. Compare 
visually the quality of fit with the density estimates you 
calculated in (i).