Originally Posted by

**mightysparks** I have no idea how to do the following question, any help is appreciated.

Among healthy adults the concentration of arsenic in the blood is normally distributed with a mean of 3.2 micrograms per decilitre (μg/dL) and a standard deviation of 1.5 μg/dL. Suspecting that groundwater in the local area might be contaminated with arsenic, a resident had her own blood sampled and the arsenic level in her blood was found to be 6.5 μg/dL. Is it reasonable for her to think that she had been exposed to arsenic contamination?