Rewrite the number: move the decimal point as required without changing the size of the original number. If it is rewritten as a unit of ten thousand, the decimal point of the original number will be shifted to the left by four places and written as a unit of ten thousand; If the unit is changed to 1 100 million, the decimal point of the original number is shifted to the left by 8 places, and the unit is written as "1 100 million".

Approximation: "rounding method": according to the requirements, according to the number on the last digit, if it is less than 5, all digits after the number will be directly removed; On the other hand, press "1" to move forward. The "one-in-one method" means that as long as there is a digit greater than 0 behind the digit to be reserved, one digit of "1" must be entered in front. All the numbers after the numbers that should be kept in the "truncation method" are deleted.