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So this is the change, B  A, relative to the starting value A, and then multiplied by 100 to express this ratio as a percent. In your case you don't have numbers A and B, you have intervals, 100 to 120 and 120 to 140. I want to look at a slightly different example. Suppose I project a range for 2007 to be between 100 and 120 and a range for 2008 to be between 130 and 140. There are two numbers you can use to determine an interval, its smallest value or base, and its length. In my example the bases of the two intervals are 100 and 130 and the lengths are 120  100 = 20 and 140  130 = 10. I could then say that the base of the range has changed
and the length has changed
In other words the base of the range has increased by 30% but the length has decreased by 50%. In your example the base of the range has increased by 20% but the length has remained unchanged. I hope this helps,  


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