A sample of ten cars was tested for fuel efficiency. The individual efficiencies (in km/l) are:
15.2, 13.8, 14.9, 14.1, 15.0, 14.5, 13.9, 14.8, 15.3, 14.7.
The mean efficiency of this sample has been found to be 14.6 km/l.
Using this information, answer the following.
(i) Calculate the variance of the fuel efficiencies.
(ii) Find the standard deviation of the efficiencies correct to two decimal places.