A flexible pavement has a 4-inch sand-mix asphalt wearing surface, 10-inch soil cement base, and a 10- inch crushed stone sub base. It is designed to withstand 400 20-kip single-axle loads and 900 35-kip tandemaxle loads per day.
The subgrade CBR is 8, the overall standard deviation is 0.45, the initial PSI is 4.2, and the final PSI is 2.5. What is the probability that this pavement will have a PSI above 2.5 after 25 years? (Drainage coefficients are 1.0.)