（1）3.8-1.9+7.2-8.1，
=（3.8+7.2）-（1.9+8.1），
=11-10，
=1；
（2）（
| 7 |
| 8 |
| 5 |
| 8 |
| 3 |
| 7 |
=
| 3 |
| 2 |
| 3 |
| 7 |
=
| 7 |
| 2 |
=
| 7 |
| 30 |
（3）40-（7.7+4.8÷1.2），
=40-（7.7+4），
=40-11.7，
=28.3；
（4）（
| 3 |
| 29 |
| 1 |
| 13 |
=
| 3 |
| 29 |
| 1 |
| 13 |
=39+29，
=68．
| 7 |
| 8 |
| 5 |
| 8 |
| 3 |
| 7 |
| 3 |
| 29 |
| 1 |
| 13 |
| 7 |
| 8 |
| 5 |
| 8 |
| 3 |
| 7 |
| 3 |
| 2 |
| 3 |
| 7 |
| 7 |
| 2 |
| 7 |
| 30 |
| 3 |
| 29 |
| 1 |
| 13 |
| 3 |
| 29 |
| 1 |
| 13 |