Question

The following table gives the percentage of on-time arrivals in U.S airports from 2004 through 2013.

Year 2004 2005 2006 2007 2008
On time arrivals/% 76.13 74.35 77.11 70.33 70.55
Year 2009 2010 2011 2012 2013
On time arrivals/% 79.69 76.75 75.46 84.93 80.33

Average - 765.63/10 = 76.563% but how do I set up the formula to find the standard deviation?

Answer 1

From Google:

To calculate the standard deviation of those numbers:
Work out the Mean (the simple average of the numbers)
Then for each number: subtract the Mean and square the result.
Then work out the mean of those squared differences.
Take the square root of that and we are done!