\[\boxed{\mathbf{2.}}\]
\[24 + 6 = 20 + (4 + 6) =\]
\[= 20 + 10 = 30\]
\[35 + 5 = 30 + (5 + 5) =\]
\[= 30 + 10 = 40\]
\[43 + 7 = 40 + (3 + 7) =\]
\[= 40 + 10 = 50\]
\[58 + 2 = 50 + (8 + 2) =\]
\[= 50 + 10 = 60\]
\[66 + 4 = 60 + (6 + 4) =\]
\[= 60 + 10 = 70\]
\[72 + 8 = 70 + (2 + 8) =\]
\[= 70 + 10 = 80\]
\[81 + 9 = 80 + (1 + 9) =\]
\[= 80 + 10 = 90\]
\[47 + 3 = 40 + (7 + 3) =\]
\[= 40 + 10 = 50\]