Thanks to Kate Owens (@katemath) for sharing a great graph and saying the phrase “standard deviation” in a tweet. I was going to teach standard deviation to my Survey of Math class the next day, so this was perfect timing. The following is how I used the graph in class. Note that in description of the graph, the standard deviation is given. This was not shown to the students until later. http://visual.ly/daylight-saving-time-explained

- How can you use the graph to figure out what day of the year has the longest night? shortest night?
- Where are the time changes? Does it really save daylight?
- What type of average (mean, median, mode, midrange) do you think is used in the graph?
- How can you use the graph to figure out which has a higher standard deviation, sunset or sunrise?
- Estimate the average sunrise time. What percent of the days have a sunrise earlier than than the average? later than the average.
- (I had two students pick two sun rises times. They were 5:20 and 6:40.) How many sunsets occur during this time?
- Who would find the above sunrise interval useful? (One idea would be construction workers or people who work outside.)
- This graph is for Chicago, IL. Would it be similar for where we live, Hickory, NC?
- As you moved closer to the equator, would the standard deviation change? What about for a location in Alaska. How would their standard deviation for sunrises be?

I guided the class through those questions in a 50 minute class period. I liked the activity because the data was in the form of a graph. Usually, the exercises list out the data and have students calculate every thing. I plan on using the graph again and making a lab exercise about it.

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