1. Rounding

Step 2: Step 1.

3. Tailing method

4. Estimation method of quantity unit

For example:

L, low estimation method: that is, only calculate the lowest bit in the formula to predict or use this method to test whether the value of the original formula is accurate. This method is often used for checking calculation. For example, in the simple algorithm of 467- 198, students often make the mistake of adding or subtracting more or less. As long as 17-8=9, the accuracy of the original formula can be predicted from the unit of the result.

2. High-order estimation: only calculate the highest order of several known numbers in the formula, and then estimate the correct rate of the whole formula according to the operation result of the highest order. For example: 4278÷73, because 4278≈4200, 73≈70, from 4200 70 = 60, we can judge whether the highest bit of the quotient is correct.

3. Digital estimation method: according to the digital principle and the positioning rule of product quotient, that is, the number of digits of product is equal to the sum of two factors or 1 is less than this sum; The number of digits of the quotient is equal to the number of digits of the dividend, and the difference obtained by subtracting the number of digits of the divisor, or less than this difference 1, is estimated, for example: 267×82=, because the number of digits of the original formula is five digits after rounding off the high digits, 3×8=24, 24 ≥10; 246×32=, because the high rounding is 2× 3 = 6,6 <10, so the number of digits of the value of the original formula is four digits, and for another example, 7298÷36= several digits, because the two digits of the four-digit subtraction of the dividend are equal to 2, and the first two digits are enough to divide, so the quotient of the original formula is three digits.

4. Approximate estimation method: For some complicated multiplication or division; In written calculations, estimates are often used as the basis. First, the known number is rounded to the approximate value of integer ten, integer hundred and integer thousand, and then the approximate value of the result is estimated. If we estimate 7832×63, because the product of 7832≈8000, 63≈60 and 8 thousand times 60 is 480,000, the 3 of 7832× rain is about 480,000. If we estimate 56427 ≈ 732, the dividend and divisor are close to 560,000 and 700,560,000 respectively.

5. Observation and estimation method: observing the known number, through estimation, we can quickly judge who is older or younger or the accuracy of calculation. For example, the comparison size is 80+20×80+200(80+20)×(80+20) and 4/7 and 5/1multiple choice question 32.7×1.5 = () A.4.905b.

6. Intuitive estimation method: After learning the measurement unit, the teacher guides the students to estimate with the help of students' intuitive perception, such as: how long is 1 meter, and how long is 100 meter? 100m? Another example is: visual inspection, step estimation, length, area, etc.

7. Mouth algorithm: In calculation, besides memorizing the addition table and multiplication formula, it is also very beneficial to memorize the calculation results of some special numbers, such as 25×4= 100, 125×8= 1000, 15× 4. 12× 12= 144 and so on. These basic oral calculations can also be used for estimation, such as 1248×8 13. Because the two known numbers in the problem are close to 1250 and 800 respectively, 128 is used.

8. Comprehensive estimation method: the observed object is regarded as a whole, and all aspects of knowledge are comprehensively used for estimation. For example, without calculation, estimate which of the following questions has the largest product and explain the reasons.

82×88 83×87 84×86 85×85