The Department of Civil Engineering at the Virginia Polytechnic Institute and State University compared a modified (M-5 hr) assay technique for recovering fecal coli forms in storm water runoff from an urban area to a most probable number (MPN) technique. A total of 12 runoff samples were collected and analyzed by the two techniques. Fecal coli form counts per 100 milliliters are recorded in the following table. Construct a 90% confidence interval for the difference in the mean fecal coli form counts between the M-5 hr and the MPN techniques. Assume that the count differences are approximately normally distributed.

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Sample MPN Count M-5 hr Count 2300 1200 450 210 270 450 154 179 192 2010 930 400 436 4100 2090 219 169 194 174 230 340 194 274 183 1234567890H卫