Note: For all questions in this assignment that require you to use a two-sample t-test, always use the non-pooled procedure (that is, the procedure that assumes population standard deviations are not equal).

Note: if your t-table does not include the correct df value, please round down to the next available df value.

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The Air Quality Index (AQI) is used to measure air quality near roadways and industrial regions in large cities. Governments report AQI values for common pollutants to keep the public informed about air quality. AQI values of 0-50 are regarded as good, 51-100 as moderate, 101-150 as unhealthy for sensitive individuals, 151-200 as unhealthy, 201-300 as very unhealthy, and beyond 300 as hazardous.

The following table gives AQI values for S02 (Sulphur Dioxide) and CO (Carbon Monoxide) from a random sample of 20 locations in California, between the years 2000 and 2010.