\[\boxed{\mathbf{194\ (194).}\mathbf{\ }Еуроки\ - \ ДЗ\ без\ мороки}\]
\[1)\ верно:\]
\[\frac{3}{8} = \frac{3 \cdot 3}{8 \cdot 3} = \frac{9}{24}\text{.\ }\]
\[2)\ неверно:\]
\[\frac{4}{5} = \frac{4 \cdot 4}{5 \cdot 4} = \frac{16}{20}\ \ \ или\ \ \ \frac{4}{5} =\]
\[= \frac{4 \cdot 5}{5 \cdot 5} = \frac{20}{25}.\]
\[3)\ неверно:\]
\[\frac{72}{90} = \frac{72\ :9}{90\ :9} = \frac{8}{10}.\]
\[4)\ верно:\]
\[\frac{42}{49} = \frac{42\ :7}{49\ :7} = \frac{6}{7}.\]
\[\boxed{\mathbf{194}\mathbf{.}}\]