Following are measurements of soil concentrations (in mg/kg) of chromium (Cr) and nickel (Ni) at 20 sites in the area of Cleveland, Ohio. These data are taken from the article €œVariation in North American Regulatory Guidance for Heavy Metal Surface Soil Contamination at Commercial and Industrial Sites€ (A. Jennings and J. Ma, J Environment Eng, 2007:587€“609).

a. Construct a histogram for each set of concentrations.

b. Construct comparative boxplots for the two sets of concentrations.

c. Using the boxplots, what differences can be seen between the two sets of concentrations?

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1 511 Cr: 34 2 574 496 322 424 269 140 244 252 76 108 24 38 18 34 30 191 Ni: 23 22 55 39 283 34 159 37 61 34 163 140 32 23 54 837 64 354 376 471