20. The following observations are amounts of hydrocarbon emissions resulting from road wear of biasbelted tires under a 522-kg load in ated at 228kPa and driven at 64km/hr for 6 hours ( Characterization of Tire Emissions Using an Indoor Test Facility, Rubber Chem. Tech., 1978: 7—25): .045, .117,

.062, and .072. What con dence levels are achievable for this sample size using the signed-rank interval?

Select an appropriate con dence level and compute the interval.