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Chapter 2: Q99. (page 117)

Lead in drinking water. The U.S. Environmental Protection Agency (EPA) sets a limit on the amount of lead permitted in drinking water. The EPA Action Level for lead is .015 milligram per liter (mg/L) of water. Under EPA guidelines, if 90% of a water system鈥檚 study samples have a lead concentration less than .015 mg/L, the water is considered safe for drinking. I (coauthor Sincich) received a recent report on a study of lead levels in the drinking water of homes in my subdivision. The 90th percentile of the study sample had a lead concentration of .00372 mg/L. Are water customers in my subdivision at risk of drinking water with unhealthy lead levels? Explain.

Short Answer

Expert verified

The water customers are not at risk of drinking water with unhealthy lead levels.

Step by step solution

01

Defining percentile

A percentile is a value below which a certain number or percentage of values or observations fall. For example, the 45th percentile indicates 45 percent of the total number of values or observations can be found.

02

Indicating the reason for not having a risk of drinking water with unhealthy lead levels.

The research study shows that 90 percent of the samples show that the lead concentration is 0.00372 mg/L (which is less than 0.15 mg/L). Due to this reason, the drinking water is safe for the water customers.

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Most popular questions from this chapter

Question: Corporate sustainability of CPA firms.Refer to the Business and Society (March 2011) study on the sustainability behaviors of CPA corporations, Exercise 1.28 (p. 51). Corporate sustainability, recall, refers to business practices designed around social and environmental considerations. Data on the level of support for corporate sustainability were obtained for 992 senior managers. The level of support was measured quantitatively. The simulation was used to convert the data from the study to a scale ranging from 0 to 160 points, where higher point values indicate a higher level of support for sustainability.

a.A histogram for level of support for sustainability is shown next. What type of histogram is produced, frequency or relative frequency?

b.Use the graph to estimate the percentage of the 992 senior managers who reported a high (100 points or greater) level of support for corporate sustainability.

Museum management. Refer to the Museum Management and Curatorship (June 2010) study of how museums evaluate their performance, Exercise 2.14 (p. 74). Recall that managers of 30 contemporary art museums identified the performance measure used most often. A summary of the results is reproduced in the table. Consider the bar graph shown. Identify two ways the bar graph might mislead the viewer by overemphasizing the importance of one of the performance measures.

Groundwater contamination in wells. In New Hampshire, about half the counties mandate the use of reformulated gasoline. This has led to an increase in the contamination of groundwater with methyl tert-butyl ether (MTBE). Environmental Science & Technology (Jan. 2005) reported on the factors related to MTBE contamination in public and private New Hampshire wells. Data were collected for a sample of 223 wells. Three of the variables are qualitative in nature: well class (public or private), aquifer (bedrock or unconsolidated), and detectible level of MTBE (below limit or detect). [Note: A detectible level of MTBE occurs if the MTBE value exceeds .2 micrograms per liter.] The data for 11 selected wells are shown in the accompanying table.

Source: Based on J. D. Ayotte, D. M. Argue, and F. J. McGarry, 鈥淢ethyl tert-Butyl Ether Occurrence and Related Factors in Public and Private Wells in Southeast New Hampshire,鈥� Environmental Science & Technology, Vol. 39, No. 1, Jan. 2005, pp. 9鈥�16

a. Use graphical methods to describe each of the three qualitative variables for all 223 wells.

b. Use side-by-side bar charts to compare the proportions of contaminated wells for private and public well classes.

c. Use side-by-side bar charts to compare the proportions of contaminated wells for bedrock and unconsolidated aquifers.

d. What inferences can be made from the bar charts, parts a鈥揷?

A qualitative variable is measured for 20 companies randomly sampled and the data are classified into three classes, small (S), medium (M), and large (L), based on the number of employees in each company. The data (observed class for each company) are listed below. ______________________________________ SSL M SM M S M S L M S SSS M L S L ----------------------------------------------------------------

a. Compute the frequency for each of the three classes.

b. Compute the relative frequency for each of the three classes.

c. Display the results, part a, in a frequency bar graph.

d. Display the results, part b, in a pie chart.

Describe how the mean compares to the median for distribution as follows:

a.Skewed to the left

b.Skewed to the right

c.Symmetric
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