\[1)\ 20\frac{1^{\backslash 4}}{2} + 1\frac{7}{8} = 21\frac{4 + 7}{8} =\]
\[= 21\frac{11}{8} = 22\frac{3}{8}\ \left( \frac{км}{ч} \right) -\]
\[по\ течению.\]
\[2)\ 20\frac{1^{\backslash 4}}{2} - 1\frac{7}{8} = 20\frac{4}{8} - 1\frac{7}{8} =\]
\[= 19\frac{12}{8} - 1\frac{7}{8} = 8\frac{5}{8}\ \left( \frac{км}{ч} \right) -\]
\[против\ течения.\]
\[Ответ:22\frac{3}{8}\ \frac{км}{ч};\ 18\frac{5}{8}\ \frac{км}{ч}.\]