\[\boxed{\mathbf{27.}}\]
\[\textbf{а)}\ 20 + 6\ :2 = 20 + 3 = 23\]
\[30 + 8\ :4 = 30 + 2 = 32\]
\[50 - 20\ :2 = 50 - 10 = 40\]
\[\textbf{б)}\ 43 + 10\ :5 = 43 + 2 = 45\]
\[22 + 15\ :3 = 22 + 5 = 27\]
\[12\ :3 + 34 = 4 + 34 = 38\]
\[58 - 16\ :2 = 58 - 8 = 50\]
\[92 - 6\ :3 = 92 - 2 = 90\]
\[88 - 12\ :3 = 88 - 4 = 84\]