well, in the chart for 2008 it has 8 hurricanes, in 2009 it has based on that bar, 3 hurricanes, the change is then 5, 8 - 3 = 5.
now if we take 8 to be the 100%, what is 5 off of it in percentage?
[tex]\bf \begin{array}{ccll}
amount&\%\\
\text{\textemdash\textemdash\textemdash}&\text{\textemdash\textemdash\textemdash}\\
8&100\\ 5&p
\end{array}\implies \cfrac{8}{5}=\cfrac{100}{p}\implies p=\cfrac{5\cdot 100}{8}\implies p = 62.5[/tex]
now in 2010, there were 12 hurricanes, whilst looking at the bar, in 2011 there were only 7, so that's a change of 5.
if we take 12 to be the 100%, what is 5 off of it in percentage?
[tex]\bf \begin{array}{ccll}
amount&\%\\
\text{\textemdash\textemdash\textemdash}&\text{\textemdash\textemdash\textemdash}\\
12&100\\
5&p
\end{array}\implies \cfrac{12}{5}=\cfrac{100}{p}\implies p=\cfrac{5\cdot 100}{12}\implies p\approx 41.67[/tex]
