People's education printing plate fourth grade mathematics decimal addition and subtraction.
1, decimal addition and subtraction:
(1) decimal point alignment, that is, the same digit alignment;
(2) Starting from the last digit, when calculating the addition, which digit adds up to ten, and the previous digit must be advanced1; When calculating subtraction, which bit is not reduced enough, it will be 1 from the previous bit.
(3) There is a 0 at the end of the number, which should generally be removed.
(4) Don't forget the decimal point.
2. The order of decimal addition and subtraction mixed operation is the same as that of integer addition and subtraction mixed operation:
(1) has no brackets and is calculated from left to right;
(2) If there are brackets, first count the brackets.
3. The law of integer operation is also applicable to decimal operation. In the operation of four decimals, proper application of the operation properties of additive commutative law, associative law and continuous subtraction will make the calculation easier.
When the number is decimal, the (ending) 0 is usually removed.
5. When integers and decimals are added and subtracted:
(1) first to the right of the integer decimal point;
(2) Add 0 with the same number as another decimal part;
(3) and then according to the calculation method of decimal addition and subtraction.
6. When the number is decimal, the (ending) 0 is usually removed.
7. Check the calculation:
Additional inspection:
(1) exchange the position of the addend and add it again to see if the result is the same as the original;
② Subtract the sum with one addend to see if the difference is the same as another addend.
Subtraction calculation:
(1) Add the subtraction and the difference by addition to see if the result is equal to the minuend;
(2) By subtraction, subtract the difference from the minuend to see if it is equal to subtraction.
Simple calculation of decimals by integer arithmetic;
The law of integer operation also applies to decimal operation. In quaternary operation, it will be easier to apply the operational properties of addition (exchange law), association law and subtraction properly.
8, simple operation method:
(1) When several decimals are added, if the mantissas of two of them can be added, the two numbers can be added first to simplify the calculation;
Such as: 0.36+18.09+2.64+4.95438+0.
(2) When a number subtracts two decimals continuously, if the sum of the two decimals can be rounded up, it is easier to add the two subtractions first and then subtract the sum of the two subtractions from the minuend;
Such as: 13.2-5.73-4.27
(3) When subtracting a number from the sum of two decimals, when the decimal part of one of these two numbers is the same as the decimal part of the minuend, you can subtract this number from the minuend first, and then subtract the other number, and the calculation is relatively simple.
Such as: 18.63-(4.75+3.63)
(4) The arithmetic of integer multiplication is also applicable to fractional multiplication.
Such as: 3.65? 42.6+3.65? 57.4
5] In the decimal operation, you can use (brackets) or (brackets) to make the calculation simple:
? Whether it is parenthesis or parenthesis.
(1) there is a plus sign in front of the brackets, and the constant sign in the brackets is removed;
Such as: 6.59-4.86+2.86
(2) The minus sign is in front of the brackets, and the total sign (plus sign becomes minus sign, minus sign becomes plus sign) is removed.
Such as: 6.47-( 1.5-0.53)
[6] In the operation at the same level without brackets, the position of exchanging data must be preceded by a symbol.
Such as: 4.95-2.67+ 1.05
A good way to learn mathematics in the fourth grade
Learn to preview and review.
Fourth-grade children should learn to preview and review regularly before class, and parents can gradually let their children form the habit of preview and review by making study plans. The key to preview is to find out your own questions about the content of the new lesson, and then listen to the teacher with questions. The key to review is to ensure that important knowledge points are remembered, that there is no doubt about what you have learned, and that every chain of mathematical knowledge is closely closed. In the process of reviewing, children should be taught to learn to sum up the experience and lessons of learning mathematics. Many fourth-grade children are reluctant to do some basic exercises of addition, subtraction, multiplication and division, but when doing homework or exams, they often miscalculate some simple operations because of carelessness. It is much more effective for children to sum up their weaknesses in the process of learning than for parents to preach. It is also a good summary method to establish a "wrong question set". Children often make mistakes in the process of doing homework and exercises. It's normal to make mistakes, but make sure you don't make the same mistakes in the future. The "wrong problem set" can record the mistakes you made for future reference.
Learn to solve problems in various ways and establish the consciousness of solving problems in simple ways.
Solving the same problem in many different ways can exercise children's divergent thinking, broaden the thinking of solving problems and better understand the basic ideas of mathematics. For example, when solving two-step and three-step application problems, train children to solve problems in different ways, such as step-by-step method, comprehensive method and equation method, and finally compare them to see which method is simpler and use the simplest method to solve problems. Simplifying complex problems is the basic idea of mathematics, which is formed by simplifying numbers and graphics in the real world. Don't use complicated methods to solve problems that can be solved by simple methods. This requires children to find simple methods when solving specific math problems. For example, when thinking about complex problems, it is simpler and clearer to use the method of assuming unknown quantities than to use direct formulas, and it is easier to use direct formulas when solving simple problems.
Pay attention to the study of basic concepts.