1, rounding
This is an accurate counting retention method, which is essentially the same as other methods. But the special point is that the difference between the reserved part and the actual value cannot exceed half of the last order of magnitude: if there is a probability of 0 ~ 9, the error sum of this method is the smallest for a large number of reserved data. This is why we use this method as the basic booking method.
2, into the law
One-step method is to add 1 to the last bit of the reserved part after removing the redundant figures. The approximation thus obtained is a residual approximation (i.e., greater than the exact value).
In our real life, rounding is not always possible, and sometimes rounding is used (that is, as long as the omitted digits are greater than zero, one digit must be entered).
In order to make the results closer to the objective reality or make the results meaningful.
3. Tailing method
Truncation is a commonly used mathematical method, which removes the decimal part of a number and takes its integer part, and its value is approximate (less than the exact value), which is often used in life. Also known as the tail cutting principle.
For example: (3.25789)≈3 (π)≈3(3.999)≈3
Tail-cutting method has many practical applications, such as the problem of "cutting cloth to make clothes" When the cloth is redundant, the decimal part is usually omitted.
4, quantity unit estimation method
Use real-life objects to perceive units of quantity and actually experience the size of data.
Knowledge points that need to be mastered in the third grade estimation:
1, the estimate is only a rough figure, not an accurate result.
2. Estimation method: First, consider a multi-digit as the nearest integer of ten, one hundred and one thousand, and then multiply it by one digit.
3. Write ""(about equal sign) in the estimated horizontal style, and add "about" to the answer.
Such as 398×6≈ (398 is 400),
203×5≈ (203 is 200), 347×2≈ (347 is 350) and 996×7≈ (996 is 1000).
4. When estimating, estimate multiple numbers, not one number.
For example: 196×8≈ estimation 196 is 200, and the estimated value is calculated with 200×8. Never estimate 8 as 10. If the difference between the estimated value and the exact value is too large, the meaning of estimation will be lost.