(1)31-8.1=1.44,
31-8.1+8.1=1.44+8.1,
31=3.64,
31÷3=3.64÷3,
1=1.18;
(8)
87
6 :1=
9
6 :8,
9
6 1=
87
6 ×8,
9
6 1=
64
6 ,
9
6 1×
6
9 =
64
6 ×
6
9 ,
1=6;
(3)31+
1
4 1=
13
16 ,
(3+
1
4 )1=
13
16 ,
13
4 1=
13
16 ,
13
4 1×
4
13 =
13
16 ×
4
13 ,
1=
1
4 ;
(4)
80
1 =
3
6 ÷3,
80
1 =
3
6 ×
1
3 ,
80
1 =
1
6 ,
1=80×6,
1=100.