in 1975 it was 1000tons, ok, well, in 1976 it went up by 10%, how much is a 10% increase?
[tex]\bf \begin{array}{ccllll}
coal&\%\\
\text{\textemdash\textemdash\textemdash}&\text{\textemdash\textemdash\textemdash}\\
1000&100\\
x&100+10
\end{array}\implies \cfrac{1000}{x}=\cfrac{100}{100+10}\implies \cfrac{1000\cdot 110}{100}=x
\\\\\\
1100=x[/tex]
well, in 1976 it was 1100 tons then, and in 1977 it went down by 5% of 1100, well, if we take 1100 to be the 100%, then what is a 5% decrease?
[tex]\bf \begin{array}{ccllll}
coal&\%\\
\text{\textemdash\textemdash\textemdash}&\text{\textemdash\textemdash\textemdash}\\
1100&100\\
x&100-5
\end{array}\implies \cfrac{1100}{x}=\cfrac{100}{100-5}\implies \cfrac{1100\cdot 95}{100}=x[/tex]
