Lifetred, Inc., makes automobile tires that have a mean life of 60,000 miles with a standard deviation of 2500 miles. a. What fraction of tires s expected to survive beyond 66,250 miles? b. What fraction will survive fewer than 57,000 miles? c. ---- (skip this) d. What length of warranty is needed so that no more than 10 percent of the tires will be expected to fail during the warranty period?