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What exactly it is meant by "average increase in percentage"? I stumble upon this term in while solving this problem:

The average monthly income and expenditure of a person in the year $1995$ is $ \$ 14,000 $ and $ \$ 11,000 $ respectively and that of the year $2000$ is $ \$ 21,000 $ and $ \$ 17,600 $ respectively.Find the average percentage increase in expenditure of the person between $1995$ and $2000$.


ADDED: The solution given in my module goes like this:

Let the cumulative increase in expenditure be $r\%$ then,

$$17,600 = 11,000 \times (1+\frac{r}{100})^5 \Rightarrow 1.6 = (1+\frac{r}{100})^5 \Rightarrow r = 10 $$

But I don't really understand,also how can we possible solve $r$ (by using hand)?For this problem they have utilized the four options given but it's a bit tedious I suppose so I am more interested in any alternative procedure if exists.

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    The question is from my data-interpretation module,it includes a line graph which i avoided here by giving the values directly.2011-01-06
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    @Jasper Loy: It is increase and I think it's pretty much clear and $r\% \Rightarrow \frac{r}{100} $ this is also trivial,I am not looking for nitpicking instead I will appreciate well explained answer.2011-01-06

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