\[\boxed{\mathbf{424.}}\]
\[1)\ a = 1:\]
\[\pi \approx 3,14\]
\[0 < 2 < \pi\]
\[0 < 1 < \frac{\pi}{2}\]
\[Ответ:\ \ I\ четверть.\]
\[2)\ a = 2,75:\]
\[\pi \approx 3,14\]
\[\pi < 5,5 < 2\pi\]
\[\frac{\pi}{2} < 2,75 < \pi\]
\[Ответ:\ \ II\ четверть.\]
\[3)\ a = 3,16:\]
\[\pi \approx 3,14\]
\[2\pi < 6,32 < 3\pi\]
\[\pi < 3,14 < \frac{3\pi}{2}\]
\[Ответ:\ \ III\ четверть.\]
\[4)\ a = 4,95:\]
\[\pi \approx 3,14\]
\[3\pi < 9,9 < 4\pi\]
\[\frac{3\pi}{2} < 4,95 < 2\pi\]
\[Ответ:\ \ IV\ четверть.\]