There is concern about the speed of automobiles traveling over a particular stretch of highway. For a random sample of 28 automobiles, radar indicated the following speeds, in miles per hour:

58 63 68 57 56 72 58 69 53 55 61 66 51 59 54 64 58 57 66 61 65 70 63 65 57 56 61 59

a. Check for evidence of nonnormality.

b. Find a point estimate of the population mean that is unbiased and efficient.

c. Use an unbiased estimation procedure to find a point estimate of the variance of the sample mean.