\[\boxed{\mathbf{1.}}\]
\[\mathbf{Левее\ расположено\ число:}\]
\[1) - 15;\]
\[2) - 7;\]
\[3) - 3,2.\]
\[\boxed{\mathbf{2.}}\]
\[1)\ |1,9| + | - 11| = 1,9 + 11 =\]
\[= 12,9\]
\[2)\ | - 20| - | - 12,4| = 20 -\]
\[- 12,4 = 7,6\]
\[3)\ |0,7| \cdot | - 0,8| =\]
\[= 0,7 \cdot 0,8 = 0,56\]
\[4)\ | - 4,8|\ :|8| =\]
\[= 4,8\ :8 = 0,6\]
\[\boxed{\mathbf{3.}}\]
\[1)\ | - 4| = 4;\ \ \ \ \ \]
\[|6| = 6 \Longrightarrow | - 4| < |6|\]
\[2)\ | - 5| = 5;\ \ \ \]
\[\text{\ \ }| - 12| = 12 \Longrightarrow | - 5| < | - 12|\]
\[3)\ |3,8| = 3,8;\ \ \ \]
\[\ |4,6| = 4,6 \Longrightarrow |3,8| < |4,6|\]
\[4)\ | - 2,4| = 2,4;\ \]
\[\text{\ \ }|5,1| = 5,1 \Longrightarrow | - 2,4| < |5,1|\]
\[\boxed{\mathbf{4.}}\]
\[|a| < 5,3;\ \ \ \ \ \ a \in Z:\]
\[a = \{ - 5, - 4, - 3, - 2, - 1,0,\ 1,\ 2,\ 3,\ 4,\ 5\}.\]