\[\boxed{\mathbf{19.}}\]
\[\textbf{а)}\ 1 + 2 \cdot 2 = 1 + 4 = 5\]
\[2 + 2 \cdot 4 = 2 + 8 = 10\]
\[3 + 3 \cdot 4 = 3 + 12 = 15\]
\[4 + 4 \cdot 3 = 4 + 12 = 16\]
\[16 - 3 \cdot 2 = 16 - 6 = 10\]
\[20 - 5 \cdot 2 = 20 - 10 = 10\]
\[17 - 4 \cdot 4 = 17 - 16 = 1\]
\[13 - 6 \cdot 2 = 13 - 12 = 1\]
\[\textbf{б)}\ 8 + 3 \cdot 3 = 8 + 9 = 17\]
\[11 - 2 \cdot 3 = 11 - 6 = 5\]
\[3 \cdot 5 - 7 = 15 - 7 = 8\]
\[6 \cdot 3 - 9 = 18 - 9 = 9\]