Acopper smelting process is supposed to reduce the arsenic content of the copper to less than 1000 ppm. let μ denote the mean arsenic content for copper treated by this process, and assume that the standard deviation of arsenic content is σ=100 ppm. the sample mean arsenic content xˉ of 75 copper specimens will be computed, and the null hypothesis h0: μ≥1000 will be tested against the alternate h1: μ< 1000. a. a decision is made to reject h0 if xˉ≤980. find the level of this test.

Farmers know that driving heavy equipment on wet soil compresses the soil and injures future crops. here are data on the "penetrability" of the same type of soil at two levels of compression. penetrability is a measure of how much resistance plant roots will meet when they try to grow through the soil. compressed soil 2.85 2.66 3 2.82 2.76 2.81 2.78 3.08 2.94 2.86 3.08 2.82 2.78 2.98 3.00 2.78 2.96 2.90 3.18 3.16 intermediate soil 3.17 3.37 3.1 3.40 3.38 3.14 3.18 3.26 2.96 3.02 3.54 3.36 3.18 3.12 3.86 2.92 3.46 3.44 3.62 4.26 use the data, omitting the high outlier, to give a 95% confidence interval for the decrease in penetrability of compressed soil relative to intermediate soil. compute degrees of freedom using the conservative method. interval: to