\[s(t) = 1 + 5t.\]
\[1)\ От\ t_{1} = 2\ до\ t_{2} = 5:\]
\[v = \frac{s(5) - s(2)}{5 - 2} =\]
\[= \frac{(1 + 25) - (1 + 10)}{3} = \frac{15}{3} = 5.\]
\[Ответ:\ \ 5.\]
\[2)\ От\ t_{1} = 0,9\ до\ t_{2} = 1:\]
\[v = \frac{s(1) - s(0,9)}{1 - 0,9} =\]
\[= \frac{(1 + 5) - (1 + 4,5)}{0,1} = \frac{0,5}{0,1} = 5.\]
\[Ответ:\ \ 5.\]