Refer to the Environmental Science & Technology (Sept. 1, 2000) study on the ammonia levels near the exit ramp of a San Francisco highway tunnel, Exercise 2.30. The data (in parts per million) for 8 days during afternoon drive-time are reproduced in the table.

a. Find the range of the ammonia levels.

b. Find the variance of the ammonia levels.

c. Find the standard deviation of the ammonia levels.

d. Suppose the standard deviation of the daily ammonia levels during morning drive-time at the exit ramp is 1.45 ppm. Which time, morning or afternoon drivetime, has more variable ammonia levels?

Data from Exercise 2.30

Three-way catalytic converters have been installed in new vehicles in order to reduce pollutants from motor vehicle exhaust emissions. However, these converters unintentionally increase the level of ammonia in the air. Environmental Science & Technology (Sept. 1, 2000) published a study on the ammonia levels near the exit ramp of a San Francisco highway tunnel. The data in the table represent daily ammonia concentrations (parts per million) on eight randomly selected days during afternoon drive-time in the summer of a recent year.

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1.53 1.50 1.37 1.51 1.55 1.42 1.41 1.48