\[\boxed{\text{732.}\text{\ }\text{еуроки}\text{-}\text{ответы}\text{\ }\text{на}\text{\ }\text{пятёрку}}\]
\[\textbf{а)}\ (20 - 3)(20 + 3) =\]
\[= 400 - 9 = 391\]
\[\textbf{б)}\ \left( 10 + \frac{1}{2} \right)\left( 10 - \frac{1}{2} \right) =\]
\[= 100 - \frac{1}{4} = 99\frac{3}{4}\]
\[\textbf{в)}\ 102 \cdot 98 =\]
\[= (100 + 2)(100 - 2) =\]
\[= 10\ 000 - 4 = 9\ 996\]
\[\textbf{г)}\ 8,6 \cdot 7,4 =\]
\[= (8 + 0,6)(8 - 0,6) =\]
\[= 64 - 0,36 = 63,64\]
\[\textbf{д)}\ 4\frac{3}{4} \cdot 5\frac{1}{4} = \left( 5 - \frac{1}{4} \right)\left( 5 + \frac{1}{4} \right) =\]
\[= 25 - \frac{1}{16} = 24\frac{15}{16}\]
\[\textbf{е)}\ 2,7 \cdot 3,3 =\]
\[= (3 - 0,3)(3 + 0,3) =\]
\[= 9 - 0,09 = 8,91\]