An experiment was conducted to determine the effectiveness of a method designed to remove oil wastes found in soil. Three contaminated soil samples were treated. After 95 days, the percentage of contamination removed from each soil sample was measured, with a mean of 49.3 percent and a standard deviation of 1.5 percent. If we wished to narrow the boundary around for a 98 percent confidence interval to within 0.5 percent, how many soil samples should be in our experiment.

437

9

6

33

3