①

1

8

+0.375

=0.125+0.375

=0.5；

②2.8÷0.7=4；

③

3

4

×0.8

=

3

4

×

4

5

=

3

5

；

④7-3

2

5

=3

3

5

；

⑤（

1

3

-

1

7

）×21

=

1

3

×21-

1

7

×21

=7-3

=4；

⑥0.04÷0.09

=

1

25

÷

9

100

=

1

25

×

100

9

=

4

9

．