x = original price, or 100%
if we take off 25% from 100% what's left is 75%, that's the discounted price.
let's then take 10% of that.
[tex]\bf \begin{array}{|c|ll} \cline{1-1} \textit{a\% of b}\\ \cline{1-1} \\ \left( \cfrac{a}{100} \right)\cdot b \\\\ \cline{1-1} \end{array}~\hspace{5em}\stackrel{\textit{75\% of "x"}}{\left( \cfrac{75}{100} \right)x\implies 0.75x} \\\\[-0.35em] ~\dotfill\\\\ \stackrel{\textit{10\% of 0.75x}}{\left( \cfrac{10}{100} \right)0.75x\implies 0.075x}~\hfill \stackrel{\textit{total percent savings}}{0.75x-0.075x\implies 0.675x} \\\\[-0.35em] ~\dotfill[/tex]
[tex]\bf \stackrel{\textit{changing that to percent format}}{0.675\cdot 100\implies 67.5\%}[/tex]
