They calculated the
compound annual growth rateCAGR = ((last number/firs tnumber)^(1/number of years))-1
The assumption is that the first year is 1.7 billion, last year is 3.6 billion and the number of years are 6, as they appear to assume that "by 2012" means 2012 is not included as a year in the calculation, giving a 7 year span. But they also excluded 2005 to give a 6 year span.
so the calculation is ((3.6 / 1.7) ^ (1/6)) -1 = 13.2%.
Still, they are off by 0.2% if you keep to 2 significant digits in the calculations and not use selective rounding. And they did fudge the span of years, making (intentional or not) the growth look better.
