\[\boxed{\mathbf{1}\mathbf{.177}}\]
\[\textbf{а)}\ 51 + 27 = 78\]
\[44 + 36 = 80\]
\[86 + 16 = 102\]
\[74 + 29 = 103\]
\[38 + 24 = 62\]
\[\textbf{б)}\ 31 - 13 = 18\]
\[46 - 23 = 23\]
\[33 - 18 = 15\]
\[74 - 37 = 37\]
\[43 - 24 = 19\]
\[\textbf{в)}\ 21 \cdot 4 = 84\]
\[49 \cdot 0 = 0\]
\[17 \cdot 2 = 34\]
\[15 \cdot 8 = 120\]
\[39 \cdot 1 = 39\]
\[\textbf{г)}\ 560\ :8 = 70\]
\[200\ :5 = 40\]
\[490\ :7 = 70\]
\[720\ :9 = 80\]
\[700\ :1 = 700\]