选择合理的方法进行计算．（1）3-14-13-34（2）7.8×1.17-7.8×0.17（3）10-712-512（4）58+45-38+15（5）0.25+1115+34+415（6）715+1921+221．-数学
| 5 |
| 12 |
=10-（
| 7 |
| 12 |
| 5 |
| 12 |
=10-1，
=9；
（4）
| 5 |
| 8 |
| 4 |
| 5 |
| 3 |
| 8 |
| 1 |
| 5 |
=
| 1 |
| 5 |
| 4 |
| 5 |
| 3 |
| 8 |
| 5 |
| 8 |
=1-
| 3 |
| 8 |
| 5 |
| 8 |
=
| 5 |
| 8 |
| 5 |
| 8 |
=1
| 1 |
| 4 |
（5）0.25+
| 11 |
| 15 |
| 3 |
| 4 |
| 4 |
| 15 |
=
| 1 |
| 4 |
| 11 |
| 15 |
| 3 |
| 4 |
| 4 |
| 15 |
=（
| 11 |
| 15 |
| 4 |
| 15 |
| 1 |
| 4 |
| 3 |
| 4 |
=1+1，
=2；
（6）
| 7 |
| 15 |
| 19 |
| 21 |
| 2 |
| 21 |
=
