First, decimals require one decimal place, which is expressed as one tenth of the exact decimal point, that is, the percentile is rounded off, and then the percentile and subsequent figures are all omitted.

2. Decimals require two decimal places, that is, decimals are accurate to hundreds, and then the numbers on thousands are rounded off. After rounding, all the other digits are omitted.

In this rounding process, if the last digit in the result is zero, it can't be omitted, which represents the precision of this decimal after rounding, so we must pay attention to it.

Third, decimals require to keep integers, that is to say, decimals are accurate to one place, so it is necessary to round the tenth digit, and then omit the tenth digit and the following digits.

By solving the above three decimal approximations, other digits can also be rounded in this way. If it is accurate to which digit, the number on the last digit will be rounded off, and then all the numbers on the next digit will be omitted.

Example:

For example, π is rounded off, leaving 3. 14. But sometimes you can use "one-in method" and "one-out method" instead of rounding. The rounded fourth house is 0, 1, 2, 3, 4, and the fifth house is 5, 6, 7, 8, 9.

For example, 288 students have a spring outing, and 45 people have a bus, which is 6.4 buses. However, you must get into a bus to avoid letting more people out and fewer cars. Because the number of cars cannot be decimal, seven buses are needed.

For another example, 10 16 liters of gasoline, if you want to refuel a car, you can add 50.8 cars on average to 20 liters, but you must remove the tail to let more cars come out and less fuel. Because the number of cars cannot be decimal, only 50 cars can be refueled.