\[Страница\ 55\]
\[\boxed{\mathbf{80.}}\]
\[1)\ 34 + 7 = 34 + 6 + 1 =\]
\[= 40 + 1 = 41\]
\[23 + 9 = 23 + 7 + 2 =\]
\[= 30 + 2 = 32\]
\[2)\ 13 + 8 = 21\]
\[37 + 5 = 42\]
\[56 + 7 = 63\]
\[48 + 4 = 52\]
\[73 + 8 = 81\]
\[65 + 9 = 74\]
\[26 + 4 = 30\]
\[32 + 8 = 40\]
\[51 + 9 = 60\]
\[\boxed{\mathbf{81.}}\]
\[6 + 5 = 11 - 7 = 4 + 10 =\]
\[= 14 - 8 = 6 + 9 = 15\]
\[\boxed{\mathbf{82.}}\]
\[9 - 6 + 3 = 6\]
\[9 + 6 + 3 = 18\]
\[9 - 6 - 3 = 0\]
\[9 + 6 - 3 = 12\]
\[60 - 20 + 10 = 50\]
\[60 - 20 - 10 = 30\]
\[60 + 20 + 10 = 90\]
\[60 + 20 - 10 = 70\]