先来重温一下如何在实数直线上四舍五入（选择性）。 写下一个带小数点的数字。 找到十分位。 找到百分位。 如果百分位上的数字等于或者大于5，那么十分位上的数值就增加。 如果百分位上的数字是4或者小于4，那么十分位保持不变。

Given the above summary, write a detailed text in English for it.
Let's ignore the decimals for a moment and try rounding to tens instead. Draw a number line from 10 to 20. The numbers on the left half of the line (like 13 or 11) are closer to 10, so they round to 10. The numbers on the right half (like 16 or 17) are closer to 20, so they round to 20. Rounding with decimals can seem confusing, but it's really the same process. You could relabel your number line as "0.10, 0.11, 0.12, ..., 0.19, 0.2" and you'd have a number line for rounding to the nearest tenth. It doesn't matter how many digits come after the decimal.   Example 1: Round 7.86 to the nearest tenth.  Example 2: Round 247.137 to the nearest tenth. The tenths place is immediately to the right of the decimal point. After rounding to the nearest tenth, this will be the final digit in your number. For now, just underline this digit.   Example 1: In the number 7.86, the 8 is in the tenths place.  Example 2: In the number 247.137, the 1 is in the tenths place. The hundredths place is the digit to the right of the decimal point. This digit tells you whether to round up or down.   Example 1: In the number 7.86, the 6 is in the hundredths place.  Example 2: In the number 247.137, the 3 is in the hundredths place. The digits to the right of the hundredths do not matter when you're rounding to the nearest tenth. They represent "extra stuff" to small to make a difference. Is the digit in the hundredths place is 5, 6, 7, 8, or 9? If it is, "round up" by adding 1 to the tenths place digit. Get rid of all digits after the tenths place, and you have your answer.  Example 1: The number 7.86 has a 6 in the hundredths place. Round up by adding 1 to the tenths place to get 7.9, removing the digits to the right. Is the digit in the hundredths place 4, 3, 2, 1, or 0? If it is, "round down" by leaving the tenth place as it is. Just remove any digits in the hundredths place and further to the right.  Example 2: The number 247.137 has a 3 in the hundredths place. Round down by removing everything past the tenths place, to get 247.1.