What to pay attention to in 3rd grade math multiplication estimation

For example, a set of tickets and tickets costs 49 yuan, and the fourth grade needs a total of 104 sets of tickets, how much money do I need to prepare?

Method 1: 49 104 5000 (RMB) 50*100

Method 2: 49 104 4500 (RMB) 45 * 100

Method 3: 49 104 5500 (RMB) 50 *110

Method 4: 49 104 5250 (RMB) 50 *105 ......

The first method of estimation is easy to calculate because 49 is 50 and 104 is 100, and 50 100 is equal to 5000. The third method of estimation, because 49 is considered to be 50 and 104 is regarded as 110, both numbers are overlooked, so that the result of the estimation 50 110 is equal to 5500, which is definitely greater than the result of 49 104, and there is a little extra money, which can prevent any accidents from happening.

The fourth estimation method, because 49 is considered to be 50 and 104 is regarded as 105, both numbers are a little bit larger, so that the result of the estimation is 50 105 equals 5250, which is very close to the exact value.

The fourth estimation method is not easy to calculate. Again, the first method of calculation is simple, and I like the first method of estimation.

Student 5: I don't think the second method is good, because if you look at 49 as 45 and 104 as 100, both numbers are small, so the result of this estimation is 45 100 is equal to 4500, and if you bring 4500 yuan, it will definitely not be enough. I like the third method of estimation.

Student 6: The first method is good, it only looks at one factor as small, and the other factor is still a little bigger, so that in the estimation results, it is okay to bring more money. …

Pay attention to the principle of estimation, pay special attention to the actual needs, choose the appropriate estimation method, and learn to adjust the estimation results according to the needs, at the same time, you can use the calculator to calculate the accurate value, so that students can have a comparison of the estimation results, and consider the more appropriate method comprehensively and optimally, not only so that students have a deeper and more accurate understanding of the estimation, but also make students have a clear grasp of the specific situation such as traveling with money to appropriately estimate larger. 】

What does it mean? Mathematics is basically about paying attention to details, and there are some methods of operation, such as multiplication and division, addition and subtraction, parentheses, brackets, and so on.

estimatedApproximate numberThere are three ways to do this:

1. Tail removal method: estimate 12 as 10 and 29 as 29.

Second, the method of entering the school: estimate 12 as 20 and 29 as 29.

3. Rounding.

Estimate 12 as 10 and 29 as 29.

In the estimation application in real life, it can be estimated large or small, and the appropriate estimation strategy should be selected according to the actual situation.

Rounding "Macro Method:

Look at one more digit than the reserved digit, the digit on the digit is "5" or greater than "5", forward one digit, the digit on the digit is "4" or less than "4", and round it off.

For example, keep one decimal place, that is. Whereas, the dust withered retains one decimal place, that is.

The principles of estimating the large and estimating the small in the third grade include the tail method, the one method, the rounding method, and the whole method.

1. Tail removal method.

That is, the mantissa of each number is removed, and the whole number is rounded ten or hundred.

For example, Oriental Travel Agency organized several tour groups during the "Eleventh" period, the situation is: 524 people in Lijiang, 208 people in Huangshan, 602 people in the Great Wall, 310 people in Jiuzhaigou, 219 people in Emeishan, how many people did the travel agency receive during the "Eleventh" period?

Remove the mantissa and add the whole hundreds to get:

500+200+600+300h20

1800 (person).

2. Advance a method.

That is, add 1 to the highest digit of each number, and round ten whole hundreds for calculation. For example:

3. Rounding method.

That is, the mantissa less than or equal to 4 is rounded, and the equal or greater than 5 is entered, and the whole ten or hundred teachings are calculated.

For example, "420 yuan per kilogram of apples, how much yuan should a kilogram of apples pay"?

The estimate is 42 1,8 4 2 = 8 (yuan).

4. Make up the ten methods.

5. Seek the whole in part.

That is, to divide a large whole into several parts equally, and find the whole number according to the number of parts, for example, to estimate the number of spectators in the stadium, first divide each stand into several parts, count how many people are in one of them, and then estimate the people of a stand, and finally calculate the number of people in the whole stand according to the number of several spectators.

Knowledge points to be mastered in the third grade estimation:

1. Estimation is only an approximation, not an exact result.

2. Estimation method: first regard the multi-digit number as a whole closest to it.

Ten, hundreds, thousands, and multiply by a single digit.

3. Write " about the equal sign in the horizontal form of estimation, and add "approximately" to the answer.

For example, 398 6 (think 398 as 400), 203 5 (think 203 as 200), 347 2 (think 347 as 350), 996 7 (think 996 as 1000).

4. Estimate multiple digits when estimating, and don't estimate single digits.

For example, 196 8 Estimate 196 as 200 and use 200 8 to calculate the estimate. Don't estimate 8 as 10, if the estimate is too different from the accuracy, it loses the meaning of the estimate.

Multiplication is generally calculated by swapping positions. It is also possible to use division.

Solution: Multiplication calculations are checked by division, for example:

15x16=240。Checking:

Or: 240 15 = 16.

So the multiplication calculation is correct.

The calculation rule of division vertical formula:

1. Divide from the high position of the dividend, how many digits there are in the divisor, just look at the first few digits of the dividend, if it is not enough to divide, look at one more person.

2. Divide to which digit of the dividend, write the quotient on which digit, if it is not enough to divide, on this digit quotient 0.

3. The remainder obtained by each division must be smaller than the divisor, and the number of the dividend-being on this digit is dropped on the right side of the remainder, and then continue to divide.

There are two methods of multiplication: one is to check whether the number is correct by multiplication, and the other is to check whether the number is correct by division.

As a simple example: 12 2 24, the method of multiplication is to exchange the two multipliers and calculate again to see if the result of the two multiplications is the same, i.e. 2 12 24. The method of division is to divide the product by one of the multipliers to see if the quotient is another multiplier, i.e. 24 2 12 or 24 12 2.

Simple multiplication

First, the combination method.

Multiplying a number by two single digits in a row, it can be rewritten in the form of multiplying this number by the product of these two numbers according to the situation, making the calculation easy. When calculating, adding a small parenthesis can make the calculation easy. Because the parentheses are preceded by a multiplier sign, there is no change in the parentheses.

Second, the decomposition method.

Multiply a number by a two-digit number, and decompose the two-digit number into two single-digit multiplication forms according to the situation, and then use this number to multiply two single-digit numbers in a row to make the calculation easy.

Third, the method of splitting numbers.

For some problems, if you do the calculation step by step, it is more troublesome, but we can flexibly use the splitting method to make simple calculations according to the characteristics of factors and other numbers.

Fourth, the number change method.

For some topics, a certain number can be transformed according to the situation to create conditions for simplifying the complex.

There are two ways to check the multiplication vertical form:

1) Product One of the factors = the other;

2) Apply the commutative law of multiplication: swap the positions of the two factors and multiply them again.

Here are some examples:

When checking the multiplication formula, you only need to switch the multiplier position and multiply it again, and the result will be the same twice.

When the multiplication equation is checked, you only need to swap the two multipliers and multiply them again, and if the result is the same twice, the calculation is correct.

For example, 12 13 = 156

The calculation process and the verification process are shown in the figure below!

1. Rounding: 0,1,2,3,4, all not carrying, 5,6,7,8,9, carrying.

2. Advance method: The advance method is to remove the number of the excess part and add 1 to the last number of the reserved part. The resulting approximation is an excess approximation (i.e., greater than the exact value).

For example, a sack can hold 200 catties of wheat, and there are 880 catties of wheat, how many sacks do you need to fill it? Divide 880 by 200, the quotient is 4, and the remainder is 80, that is, it is impossible to use 4 sacks, so it is necessary to use the further method to use 5 sacks to finish.

3. Tail removal method: The tail removal method is a common mathematical value method of removing the decimal part of the number and taking the integer part, and the value is an approximate value (that is, smaller than the exact value), which is often used in life.

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