1, rounded: 0, 1, 2, 3, 4 without carry, 5, 6, 7, 8, 9 carry.

2. One-to-one method: One-to-one method is to add 1 to the last number of the reserved part after removing the redundant number, so that the approximate value obtained is surplus (that is, greater than the accurate value).

3. Truncation method: Truncation method is a commonly used mathematical method, which removes the decimal part of a number and takes its integer part, and its value is approximate (that is, less than the exact value), which is often used in life.

4. Quantity unit estimation method: use real-life objects to perceive the quantity unit and size of actual empirical data.