Four operations of mathematics knowledge points in grade four
1, addition, subtraction, multiplication and division are called four operations.
2. In the formula without brackets, if there is only addition, subtraction or multiplication and division, it should be calculated from left to right.
3. There are multiplication, division and addition and subtraction in the formula without brackets, and multiplication and division must be calculated first, then addition and subtraction.
4. If there are brackets in the formula, count the inner side of brackets first, and then the outer side of brackets; The calculation order of the formulas in brackets follows the above calculation order.
5, multiply first and then divide, then add and subtract, with brackets, calculate in advance.
On the operation of "0"
1 and "0" are inseparable; Letter means: 0 error.
2. Add 0 to a number to get the original number; The letter means: A+0 = A.
3. Subtract 0 from a number to get the original number; The letter means: a-0 = a.
4. The minuend is equal to the minuend, and the difference is 0; Letter: a-a=0
5, a number multiplied by 0, still get 0; Letter: a×0=0
6. Divide 0 by any number other than 0 to get 0; The letter means: 0÷a(a≠0)=0.
7,0 ÷ 0 can't get the fixed quotient; 5÷0 can't get the business. (meaningless)
The fourth grade first volume mathematics "approximate" knowledge point approximate knowledge point.
1, the characteristics of exact number and approximate number.
The exact number is generally in the unit of "one", and the approximate number is in the unit of "ten thousand" or "one hundred million", and the mantissa is omitted.
2. Use rounding method to keep approximate values.
Look at the next number to be reserved according to the requirements in the question. If this number exceeds 5, proceed to the previous number. If it is less than 5, give it up. Regardless of the last few digits of the mantissa. If it is accurate to 10 thousand digits, only a few thousand can be seen, and if it is accurate to 100 million digits, only tens of millions can be seen. Finally, be sure to write the name of the company.
Typical exercise
fill (up) a vacancy
1, a number consists of seven thousands, three hundreds and five tens, and this number is ().
2. From the right, the hundredth place is (), and the fifth place is ().
3. 3465 digits are () digits, which are () digits. "6" is in the () position, which means (). "3" is in the position of (), which means ().
4. There is () ten in 100, () hundred in 1000, and () one in10.
The four digits of 5 are (), and the three digits of 5 are (). Their sum and difference are (). It consists of () thousand, () hundred and () one.
6. The reading method of numbers within10000 is to read in numerical order from () bit; () How many students are there? () thousands; What are the hundreds of students who participated in ()? There are one or two zeros in the middle, which are read-only () zeros; No matter how many zeros () are at the end.
Second, write down the approximate figures of the following figures.
The divisor of 698 is: the divisor of 2956 is:
The divisor of 3 120 is:
The divisor of 1004 is:
The method of multiplying three numbers by two numbers of the fourth grade mathematics knowledge point 1;
Multiply each bit of one factor by each bit of another factor in turn, and then multiply each bit of another factor by ten bits of this factor in turn. When you multiply to which bit, the single bit of the product will be aligned with which bit. When a bit exceeds ten, it will advance to "1" and then add the products of the two multiplications. When there is a zero at the end, align the numbers in front of the two factors 0, multiply them, and then add a few zeros that did not participate in the operation after the product. When there is a 0 in the middle, this 0 will participate in the operation.
2. Variation law of factor and product: If one factor remains unchanged, another factor will be expanded (or reduced) several times, and the product will also be expanded (or reduced) by the same multiple.
3. Estimation method of multiplication of two or three digits: first omit the mantissa behind the digits of two factors, find the divisor, and then multiply the two divisors.
Supplementary knowledge points
1, estimation method: use rounding method to estimate. Is this estimate big or small? That is, the method of estimation;
2. Calculate three digits multiplied by two digits vertically. Note that the end of the product in the second step is written in ten digits.
3. Multiply three digits with zero in the middle or at the end of the factor by two digits.
Multiply the middle by a factor of 0; If there is a zero at the end, align the last digit of the number in front of the two factors, multiply it by the number in front of zero, and then it will return to zero, and several zeros will return to several zeros.
Estimation in real life:
Practical problems in life (is it estimated to be big or small? )
A: 350 students are going out to visit. There are 7 carriages with 56 seats each. How many cars do you need?
B, the bridge weighs 3 tons, the goods are 6 boxes, each box weighs 285 kilograms, and the car weighs 986 kilograms. Can this car cross the road?
Learning point
Methods and precautions of estimation: the coefficient should be estimated as integer ten, integer hundred or integer thousand. When estimating, pay attention to seeking truth from facts and approach the accurate value.
Math learning methods and skills in the fourth grade master the small skills in learning.
1, grab the classroom. Science study focuses on weekdays and is not suitable for surprise review. The most important thing in studying on weekdays is classroom knowledge. Listen attentively and keep your thoughts close to the teacher. At the same time, it should be pointed out that many students tend to ignore the mathematical thinking methods mentioned by teachers and pay attention to the solution of problems. In fact, thinking methods such as "combination of numbers and shapes" are far more important than the solution of a topic.
2. High-quality operation The so-called high quality refers to high precision and high speed. When writing homework, I sometimes review the same type of topic over and over again. At this time, we should consciously examine our speed and accuracy of solving problems, and after each completion, we can have a deeper thinking on such topics, such as the content it examines, the thinking and skills used in solving problems, and so on. In addition, the thinking questions assigned by the teacher should also be carefully completed. If not, don't give up easily. You should carry forward the spirit of nailing, meditate whenever you have time, and inspiration will always come to you suddenly. Most importantly, this is an opportunity to challenge yourself. Success can bring self-confidence, which is very important for learning mathematics; Even if you fail, this question will leave a deep impression on you.
3. Think hard and ask more questions. First of all, for the laws and theorems given by the teacher, we should know not only "what" but also "why", so as to get to the bottom of it. This is the best way to understand. Secondly, you should be skeptical about learning any subject, especially science. Questions about the teacher's explanation should be raised in time and discussed with the teacher. In short, thinking and asking questions are the best ways to eliminate hidden dangers in learning.
4. Summarize and compare, and clear your mind.
(1) summary and comparison of knowledge points. After learning each chapter, you should make a frame diagram of the content of this chapter or go through it in your mind to clarify the relationship between them. Similar and confusing knowledge points need to be classified and compared, and sometimes they can be distinguished by association.
(2) Summary and comparison of topics. Students can set up their own question bank. If you set up two problem sets. One is wrong and the other is accurate. For the usual homework, if there are mistakes in the exam, write them down selectively and make entries in red notes. Just read what is written in red pen before the exam. There are also some extremely clever or difficult problems written down, and all the methods and ideas of this problem are also marked in red pen. In the long run, I can sum up some types of problem-solving rules and write them down in red notes. Finally, they will become your precious wealth and help your math study.
5. Do extracurricular exercises seriously. Spare time is very precious to our students, so we should do extracurricular exercises accurately. As long as we do three or two pages carefully every day, over time, you will be able to "build a sand tower" in math learning and achieve fruitful results. Learning methods are important, but the spirit of studying hard and striving for perfection is more important. As long as you keep working hard, you will learn math well. Believe in yourself, math will make your wisdom more dazzling!
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