receives a shipment of batteries from Grenland Energy, a battery manufacturer in Skien, Norway, and tests a random sample of nine before agreeing to take it. Kongsberg is concerned that the true mean lifetime for all batteries in the shipment should be at least 50 hours. From past experience it is safe to conclude that the population distribution of lifetimes is normal with a standard deviation of 3.6 hours. For one particular shipment the mean lifetime for a sample on 16 batteries was 48.8 hours. Test at the 10% level the null hypothesis that the population mean lifetime is at least 50 hours.