（1）91×
| 1 |
| 17 |
=91×
| 1 |
| 17 |
| 1 |
| 17 |
| 1 |
| 17 |
=（91+9-100）×
| 1 |
| 17 |
=0×
| 1 |
| 17 |
=0；
（2）0.38×7−
| 19 |
| 50 |
| 19 |
| 50 |
=0.38×7-0.38+4×0.38，
=0.38×（7-1+4），
=0.38×10，
=3.8；
（3）2100÷[56×(
| 3 |
| 7 |
| 3 |
| 8 |
=2100÷[56×
| 3 |
| 7 |
| 3 |
| 8 |
=2100÷[24-21]，
=2100÷3，
=700；
（4）[(
| 2 |
| 3 |
| 1 |
| 4 |
| 5 |
| 6 |
| 1 |
| 2 |
| 3 |
| 4 |
=[
| 5 |
| 12 |
| 5 |
| 6 |
| 1 |
| 2 |
| 3 |
| 4 |
=[
| 5 |
| 12 |
| 6 |
| 5 |
| 1 |
| 2 |
| 3 |
| 4 |
=[
| 1 |
| 2 |
| 1 |
| 2 |
| 3 |
| 4 |
=1×
| 3 |
| 4 |
=
| 3 |
| 4 |