章节大纲

  • 常规

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  • 四舍四舍四舍四舍

    Two people on a boat, one holding a fishing rod and the other a landing net.

    Have you ever been fishing?
    ::你钓过鱼吗?

    People who fish often are a little unreliable when it comes to describing what they caught and how much it weighed. It’s easier to say your fish weighed ten pounds than it is to accurately describe the weight of 8 pounds 11 ounces. Ten pounds is “close enough” when you are talking about your catch.
    ::钓鱼者在描述他们捕获的鱼及其重量时往往有点不可靠。 说说你的鱼重10磅比准确描述8磅11盎司的重量容易得多。 当你谈论捕获量时,10磅“足够接近 ” 。

    Rounding

    ::四舍四舍四舍四舍

    Before dealing with the specifics of the rules for determining the in a calculated result, we need to be able to round numbers correctly. To round a number, first decide how many significant figures the number should have. Once you know that, round to that many digits, starting from the left. If the number immediately to the right of the last significant digit is less than 5, it is dropped and the value of the last significant digit remains the same. If the number immediately to the right of the last significant digit is greater than or equal to 5, the last significant digit is increased by 1.
    ::在处理用于确定计算结果的规则细节之前,我们需要能够正确四舍五入数字。对于一个数字,首先决定数字应该有多少重要数字。一旦你知道从左转到多位数,从左转到多位数,从左转到多位数。如果数字直接到最后一个重要位数右边小于5,则下调,最后一位重要位数的价值保持不变。如果数字直接到最后一个重要位数右边大于或等于5,则最后一个重要位数增加1。

    Consider the measurement 207.518 m. Right now, the measurement contains six significant figures. How would we successively round it to fewer and fewer significant figures? Follow the process as outlined in Table .
    ::考虑207.518米的测量。现在,该测量包含6个重要数字。我们如何依次将它四舍五入到数量越来越少的重要数字?遵循表6中概述的进程。

    Number of Significant Figures Rounded Value Reasoning
    6 207.518 All digits are significant
    5 207.52 8 rounds the 1 up to 2
    4 207.5 2 is dropped
    3 208 5 rounds the 7 up to 8
    2 210 8 is replaced by a 0 and rounds the 0 upto 1
    1 200 1 is replaced by a 0

    Notice that the more rounding is done, the less reliable to figure is. An approximate value may be sufficient for some purposes, but scientific work requires a much higher level of detail.
    ::但科学工作需要更详细得多的细节。

     

    Summary
    ::摘要

    • Rounding involves the adjustment of a value to account for the proper number of significant digits.
      ::四舍五入涉及调整一个数值,以计及重要数字的适当数字。
    • Rules exist for rounding of numbers.
      ::数字四舍五入有规则。

    Review
    ::回顾

    1. Why do we round numbers?
      ::为什么我们用圆数来计算?
    2. What do we need to know before we round a number?
      ::我们要先知道什么才能用数字?
    3. What is “rounding up”?
      ::什么是“整顿”?
    4. What is “rounding down”?
      ::什么是“四舍五入”?