7. The Pitney Pipe Company is one of several domestic manufacturers of PVC pipe. The quality control department sampled 600 10-foot lengths. At a point 1 foot from the end of the pipe, they measured the outside diameter. The mean was 14.0 inches and the standard deviation 0.1 inches. a. If the shape of the distribution is not known, at least what percent of the observations will be between 13.85 inches and 14.15 inches?