The article "Effect of Granular Subbase Thickness on Airfield Pavement Structural Response" (K. Gopalakrishnan and M. Thompson, Journal of Materials in Civil Engineering, 2008:331-342) presents a study of the effect of the subbase thickness on the amount of surface deflection caused by aircraft landing on an airport runway. In six applications of a 160 kN load on a runway with a subbase thickness of 406 mm, the average surface deflection was 3.24 mm with a standard deviation of 0.50 mm.
a. Can you conclude that the mean surface deflection is greater than 3 mm?
b. Can you conclude that the mean surface deflection is greater than 2.5 mm?