(1)设这个数是x,
2x+
4
5 =1,
2x+
4
5 -
4
5 =1-
4
5 ,
2x=
1
5 ,
2x÷2=
1
5 ÷2,
x=
1
10 ;
答:这个数是
1
10 .
(2)(80-9.8)×0.6-2.12,
=70.2×0.6-2.12,
=42.12-2.12,
=40.
答:差是40.
(1)设这个数是x,
2x+
4
5 =1,
2x+
4
5 -
4
5 =1-
4
5 ,
2x=
1
5 ,
2x÷2=
1
5 ÷2,
x=
1
10 ;
答:这个数是
1
10 .
(2)(80-9.8)×0.6-2.12,
=70.2×0.6-2.12,
=42.12-2.12,
=40.
答:差是40.