20．口算：
0 157410 157418 157424 157428 157434 157436 157440 157446 157448 157454 157460 157464 157466 157470 157476 157478 157484 157488 157490 157494 157496 157500 157502 157504 157505 157506 157508 157509 157510 157512 157514 157518 157520 157524 157526 157530 157536 157538 157544 157548 157550 157554 157560 157566 157568 157574 157578 157580 157586 157590 157596 157604 199269
| 180÷6= | 30×40= | 360÷3= | 72÷3= |
| 23×30= | 125÷5= | 960÷4= | 80×60= |
| 200÷8= | 770÷7= | 43×20= | 170×30= |
| 118÷6≈ | 98×19≈ | 39×49≈ | 570÷7≈ |
