1 00:00:00,050 --> 00:00:02,710 珍奈尔正在为公路赛训练 2 00:00:02,710 --> 00:00:06,000 她的计步器记录了每天她跑的距离 3 00:00:06,000 --> 00:00:08,510 这是她四天来计步器的读数： 4 00:00:08,510 --> 00:00:13,010 周六 3.89英里 周日 5.1英里 5 00:00:13,010 --> 00:00:18,010 周一 10.21英里 周二 3.35英里 6 00:00:18,010 --> 00:00:21,860 估算四天来她跑的里程数 7 00:00:21,860 --> 00:00:23,710 然后计算出准确数值 8 00:00:23,710 --> 00:00:25,130 先来估算一下 9 00:00:25,130 --> 00:00:27,410 我就把它们都四舍五入取整 10 00:00:27,410 --> 00:00:30,320 3.89 约等于4英里 11 00:00:30,320 --> 00:00:32,120 因为十分位上 12 00:00:32,120 --> 00:00:34,510 是8 大于5 13 00:00:34,510 --> 00:00:38,230 所以大约就等于4英里 14 00:00:38,230 --> 00:00:39,930 然后看5.1 15 00:00:39,930 --> 00:00:43,000 因为1小于5 所以要下舍 16 00:00:43,000 --> 00:00:45,030 近似为5英里 17 00:00:45,030 --> 00:00:51,920 10.21 因为2小于5 18 00:00:51,920 --> 00:00:53,410 要下舍到5英里 19 00:00:53,410 --> 00:00:55,990 3.35 近似为3英里 20 00:00:55,990 --> 00:00:58,720 因为3比5小 还是要下舍 21 00:00:58,720 --> 00:01:00,490 近似成3英里 22 00:01:00,490 --> 00:01:04,000 如果加起来的话 4+5=9 23 00:01:04,000 --> 00:01:07,010 9+10=19 24 00:01:07,010 --> 00:01:11,000 19+3=22 25 00:01:11,000 --> 00:01:20,000 所以我的估算结果是4天来她跑了22英里 26 00:01:20,000 --> 00:01:21,000 这是我的估算结果 27 00:01:21,000 --> 00:01:24,020 下面来计算一下准确数值 28 00:01:24,020 --> 00:01:25,540 向下拖动点 29 00:01:25,540 --> 00:01:32,680 3.89+5.1-- 30 00:01:32,680 --> 00:01:34,000 在小数相加的时候一定要注意 31 00:01:34,000 --> 00:01:36,700 要把小数点对齐 32 00:01:36,700 --> 00:01:44,390 10.21+3.35 33 00:01:44,390 --> 00:01:47,090 把这些都加起来 34 00:01:47,090 --> 00:01:52,050 先看百分位 35 00:01:52,050 --> 00:01:56,080 第二个数没有百分位 所以9+0+1=10 36 00:01:56,080 --> 00:01:59,030 10+5=15 37 00:01:59,030 --> 00:02:04,810 写5 进1 38 00:02:04,810 --> 00:02:06,450 换个颜色 39 00:02:06,450 --> 00:02:10,000 1+8=9 40 00:02:10,000 --> 00:02:12,000 9+1=10 41 00:02:12,000 --> 00:02:14,010 10+2=12 42 00:02:14,010 --> 00:02:17,020 12+3=15 43 00:02:17,020 --> 00:02:18,610 写5 44 00:02:18,610 --> 00:02:21,000 进1 45 00:02:21,000 --> 00:02:22,650 1+3=4 46 00:02:22,650 --> 00:02:25,010 4+5=9 47 00:02:25,010 --> 00:02:26,710 9+0=9 48 00:02:26,710 --> 00:02:33,040 9+3=12 49 00:02:33,040 --> 00:02:34,050 写2 50 00:02:34,050 --> 00:02:35,080 进1 51 00:02:35,080 --> 00:02:37,150 进位写在上边 52 00:02:37,150 --> 00:02:39,040 不要误认为是这些加数的一部分 53 00:02:39,040 --> 00:02:42,030 然后1+1=2 54 00:02:42,030 --> 00:02:43,850 还要注意 55 00:02:43,850 --> 00:02:46,000 这里是小数点 56 00:02:46,000 --> 00:02:52,550 所以她跑过的准确距离是22.55英里 57 00:02:52,550 --> 00:02:54,210 我们的估算还是比较接近的 58 00:02:54,210 --> 00:02:55,750 22英里 59 00:02:55,750 --> 00:02:57,360 跟准确值非常接近 60 00:02:57,360 --> 00:03:00,030 误差比半英里多一点