$\begin{array}{l}
\left( {1 + \frac{2}{3} - \frac{1}{4}} \right).{\left( {\frac{4}{5} - \frac{3}{4}} \right)^2}\\
= \left( {\frac{{12}}{{12}} + \frac{8}{{12}} - \frac{3}{{12}}} \right).{\left( {\frac{{16}}{{20}} - \frac{{15}}{{20}}} \right)^2}\\
= \frac{{12 + 8 - 3}}{{12}}.{\left( {\frac{1}{{20}}} \right)^2} = \frac{{17}}{{12}}.\frac{1}{{400}} = \frac{{17}}{{4800}}
\end{array}$
