let's first off convert those mixed fractions to improper fractions, then get their difference.
[tex]\bf \stackrel{mixed}{1\frac{1}{2}}\implies \cfrac{1\cdot 2+1}{2}\implies \stackrel{improper}{\cfrac{3}{2}}~\hfill \stackrel{mixed}{2\frac{1}{10}}\implies \cfrac{2\cdot 10+1}{10}\implies \stackrel{improper}{\cfrac{21}{10}} \\\\[-0.35em] \rule{34em}{0.25pt}\\\\ \cfrac{21}{10}-\cfrac{3}{2}\implies \stackrel{\textit{using the LCD of 10}}{\cfrac{(1)21-(5)3}{10}}\implies \cfrac{21-15}{10}\implies \cfrac{6}{10}\implies \cfrac{3}{5}[/tex]
now, the original amount, 3/2, if that is the 100%, what is 3/5 off of it in percentage?
[tex]\bf \begin{array}{ccll} amount&\%\\ \cline{1-2}\\ \frac{3}{2}&100\\\\ \frac{3}{5}&x \end{array}\implies \cfrac{~~\frac{3}{2}~~}{\frac{3}{5}}=\cfrac{100}{x}\implies \cfrac{3}{2}\cdot \cfrac{5}{3}=\cfrac{100}{x}\implies \cfrac{5}{2}=\cfrac{100}{x} \\\\\\ 5x=200\implies x=\cfrac{200}{5}\implies x=40[/tex]
