Civil engineers responsible for the design as well as maintenance of aircraft pavements traditionally use pavement-quality concrete. A study was conducted to access the suitability of concrete blocks as a surface for aircraft pavements. The original pavement-quality concrete of the western end of a runway was overlaid with 80-mm-thick concrete blocks. A series of plate-bearing tests was carried out to determine the load classification number (LCN), a measure of breaking strength, of the surface. Let RV X represent the mean LCN of a sample of 25 concrete block sections on the western end of the runway. Prior to resurfacing, the mean LCN of the original payment-quality concrete of the western end of the runway was known to be 60 with standard deviation ? = 10. If the mean strength of the new concrete block surface is no different from that of the original surface, find the probability that the sample mean LCN of the 25 concrete block sections exceeds 65.