One of the lines of pharmaceutical company produces oxygen tanks for breathing. The company is concerned that the true mean length for one tank should be at least 30 hours. From experience it is safe...

One of the lines of pharmaceutical company produces oxygen tanks for breathing. The

company is concerned that the true mean length for one tank should be at least 30 hours.

From experience it is safe to conclude that the population distribution of the oxygen

tanks’ lifetime is normal with a standard deviation of 3 hours. A shipment of nine oxygen

tanks was tested and the mean length for a sample of nine tanks was 28 hours.

a. Test at the 10% level the null hypothesis that the population mean lifetime of the

oxygen tanks is at least 30 hours.
b. Find the p-value for this test.?