(05.05 MC) An environmental group is conducting a study to determine whether lobsters in a certain region are ingesting unhealthy levels of mercury. A marine biologist classifies mercury levels greater than 6.5 parts per million as unhealthy. The mercury levels of a random sample of 25 lobsters in the region are measured and recorded, and the data are shown in the stemplot.

Stemplot for Mercury Levels. 2|2 4; 3|1 4; 3|5 8; 4|0 2; 4|5 6; 5|0 1 3 3 4; 5|6 8 9; 6|3 4; 6|6 7 8; 7|1 2.

Key: 2|2 = 2.2 parts per million

Part A: What proportion of lobsters in the sample have mercury levels classified by the marine biologist as unhealthy? (3 points)

Part B: The mean mercury level of the 25 lobsters in the sample is 5.05 parts per million and the standard deviation is 1.45 parts per million. Construct and interpret a 90% confidence interval for the mean mercury level of lobsters in the region. (5 points) (8 points)