19．不改变数的大小，将下面各数改写成三位小数．
| 2.08= | 7.1000= | 3= |
| 20= | 12.0500= | 2.1000= |
18．化简下面各数．
0 158403 158411 158417 158421 158427 158429 158433 158439 158441 158447 158453 158457 158459 158463 158469 158471 158477 158481 158483 158487 158489 158493 158495 158497 158498 158499 158501 158502 158503 158505 158507 158511 158513 158517 158519 158523 158529 158531 158537 158541 158543 158547 158553 158559 158561 158567 158571 158573 158579 158583 158589 158597 199269
| 0.020= | 1.3800= | 3.030= |
| 0.10100= | 20.0020= | 10.10= |
