The Air Transport Association of America publishes figures on the busiest airports in the United States. The following frequency distribution has been constructed from these figures for a recent year. Assume these are population data.

Number of Passengers

Arriving and Departing Number of

(Millions) ........Airports

20–under 30 ........8

30–under 40 ........7

40–under 50 ........1

50–under 60 ........0

60–under 70 ........3

70–under 80 ........1

a. Calculate the mean of these data.

b. Calculate the mode.

c. Calculate the median.

d. Calculate the variance.

e. Calculate the standard deviation.