What are the average E. coli counts for each sand level? Are the counts higher or lower with the higher level of sand in the filter? Also give the standard deviations for the E. coli counts for each sand level.

As mentioned earlier, sand is used in the filter. Different filters had different amounts of sand.

The students split the filters into two groups: those that had more than 2 inches of sand and those that had less. We will explore whether this difference results in different E. coli counts when filtering the water. In this sample, we have results from 20 filters, 14 with more than 2 inches of sand and 6 with less than 2 inches of sand. (See data file Ecoli-sand.)