Round the number 18 to the nearest ten.
A round number is a multiple of 10, 100, 1,000, and so on. Round numbers are used instead of precise ones to give the general idea of a quantity or proportion. 整十，整百，整千…的数
If you round an amount up or down, or if you round it off, you change it to the nearest whole number or nearest multiple of 10, 100, 1000, and so on. 四舍五入
A number is a word such as “two,” “nine,” or “twelve,” or a symbol such as 1, 3, or 47. You use numbers to say how many things you are referring to or where something comes in a series. 数字; 号码
The near one of two things is the one that is closer. (二者中) 离得近些的
The process of rounding
Rounding is a process by which you can write a long number as a shorter number with roughly the same value. The tenths decimal place is the digit immediately to the right of the decimal point, such as the 5 in 12.578, so to round it out you need to look at the number to its right, which is the hundredths decimal place.
Once you round a number up or down, it loses the precision it once had so if you do additional calculations with it, the resulting number can only be as precise as the tenth decimal place. In most cases you should round out the resulting number to the tenth decimal place as well.