An inner city open space area is suspected to have high levels of lead (Pb) in i
ID: 2979740 • Letter: A
Question
An inner city open space area is suspected to have high levels of lead (Pb) in its surface soil. The region of concern is 400 square meters in area and has the shape shown in the figure. (below) The region is gridded as shown (half meter by half meter). 5 gribs are selected at random (there were 72 partial grids which are excluded from the population). After removing rocks and other debris from each sample, they are weighed and three 1 gm subsamples are selected from each primary sample. These 1 gm samples are analyzed and the mass of Pb (in micrograms) in each 1 gm sample is determined. Measurement errors are assumed negligible. The data are given in Table 1.
Figure:
Table 1.
a) Estimate the mean concentration of Pb and the total mass of Pb present in this region. Calculate standard errors.
b) For comparison, calculate the sample mean and variance using simple random sampling. Then from these, calculate the estimates for inventory (I hat) and Variance s^2(I hat).
c) Apply composting to the 3 (sub)samples from each grid (see Table 1). Calculate the same set of parametere: the overall sample mean, its variance and inventory mean with variance.
Explanation / Answer
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