I think you wanted to write 'What is 5% of 100?' -that is the only way the exercices of this type can be solved. :)
[tex]5\% \ of \ 100= \\\\ =\frac{5}{100}*100= \\\\ = \frac{5}{1}*1= \\\\ = \boxed{5}[/tex]
For example you may have an exercice like this: Find the percentage of the change. Original:54 New:45
[tex]p\to percentage \\\\ p\% \ of \ 54=45 \\\\ \frac{p}{100}*54=45 \\\\ \frac{p}{100}=\frac{45}{54} \\\\ \frac{p}{100}=\frac{5}{6} \\\\ p=\frac{100*5}{6} \\\\ p=\frac{50*5}{3} \\\\ p=\frac{250}{3} \\\\ \boxed{p=83.3\%}[/tex]
