Macmillan Learning Radon is a naturally occurring gas and is the second leading cause of lung cancer in the United States. It comes from the natural breakdown of uranium in the soil and enters buildings through cracks and other holes in foundations. Radon is found throughout the United States, but levels vary considerably from state to state. Several methods can reduce the levels of radon in a home, and the Environmental Protection Agency recommends using one of them if the measured level in a home is above 4 picocuries per liter. Four readings from Franklin County, Ohio, where the county average is 8.2 picocuries per liter, were 3.8, 1.9, 12.1, and 14.4. (a) Find the mean step-by-step. That is, find the sum of the four observations and divide by 4. Give your answer for the sum to one decimal place. sum Give your answer for the mean to two decimal places. mean picocuries per liter picocuries per liter