1. A sample of 100 fluorescent light tubes from the Short Life Company has a mean life of 20.5 hours and a standard deviation of 1.6 hours. Test:

a) At the 1% level whether the sample comes from a population with mean 23.2 hours.

b) At the 5% level whether it comes from a population with mean 20.8 hours.

c) At the 5% level whether it comes from a population with mean less than 20.8 hours.