Question:

The following data represent ozone readings, in parts per million (ppm), taken at 3:00 p.m. for a random sample of 18 days.

12 34 8 15 11 18 10 21 12

13 14 17 4 8 20 9 40 21

1. Construct a stem-and-leaf display for these data. Place the leaves in ascending order.
2. In what direction, if any, are the data skewed?
3. Calculate the mean ozone reading.
4. Calculate the standard deviation of ozone readings. Use the short-cut formula.
5. Calculate the quartiles and the interquartile range.
6. Sketch a box-and-whisker plot on the graph paper below. Indicate any outliers.
7. Within what range do the middle 50% of ozone readings fall?
8. Calculate the approximate value of the 70th percentile. What does this number tell you?
9. What is the percentile rank of an ozone reading of 15? What does this number tell you?

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