2.从某玉米种子中抽取6批,在同一条件下进行发芽试验,有关数据如下:
根据以上数据可以估计,该玉米种子发芽的概率约为0.80(精确到0.10).
| 种子粒数 | 100 | 400 | 800 | 1000 | 2000 | 5000 |
| 发芽种子粒数 | 85 | 318 | 652 | 793 | 1604 | 4005 |
| 发芽频率 | 0.850 | 0.795 | 0.815 | 0.793 | 0.802 | 0.801 |
18.若a2+b2=3,ab=1,则(a+b)2的值为( )
| A. | 3 | B. | 4 | C. | 5 | D. | 9 |
17.某种细菌用肉眼是根本看不到的,用显微镜测其直径大约是0.000005米,将0.000005用科学记数法表示为( )
0 297473 297481 297487 297491 297497 297499 297503 297509 297511 297517 297523 297527 297529 297533 297539 297541 297547 297551 297553 297557 297559 297563 297565 297567 297568 297569 297571 297572 297573 297575 297577 297581 297583 297587 297589 297593 297599 297601 297607 297611 297613 297617 297623 297629 297631 297637 297641 297643 297649 297653 297659 297667 366461
| A. | 50×10-7 | B. | 50×10-5 | C. | 50×10-3 | D. | 5×10-6 |