The US Environmental Protection Agency EPA advocates a maxim

The U.S. Environmental Protection Agency (EPA) advocates a maximum arsenic level in water of 10 micrograms per litre. Below are results of EPA tests on randomly chosen wells in a suburban Michigan county. Research question: Is the mean arsenic level affected by well depth and/or age of well? (LO 2 & 3) Arsenic Arsenic Level in Wells (micrograms per litre) Age of Well (years) Well Depth Under 10 10 to 19 20 and Over Shallow 5.4 6.1 6.8 4.3 4.1 5.4 6.1 5.8 5.7 Medium 3.4 5.1 4.5 3.7 3.7 5.5 4.3 4.4 4.6 Deep 2.4 3.8 3.9 2.9 2.7 2.9 2.7 3.4 4.0

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