People's education printing plate fifth grade mathematics review data decimal multiplication.
1, decimal times integer: meaning-a simple operation to find the sum of several identical addends.
For example, 1.5×3 indicates how many times 1.5 or how many three 1.5 are.
Calculation method: first expand the decimal into an integer; Calculate the product according to the law of integer multiplication; Look at a factor * * *, how many decimal places there are, and count the decimal points from the right side of the product.
2. Decimal multiplied by decimal: meaning-that is, what is the fraction of this number.
For example, if the integer part of 1.5×0.8 is 0, what is eight tenths of 1.5?
The integer part of 1.5× 1.8 is either 0 or 1.8 times 1.5.
Calculation method: first expand the decimal into an integer; Calculate the product according to the law of integer multiplication; Look at a factor * * *, how many decimal places there are, and count the decimal points from the right side of the product.
Note: In the calculation results, the 0 at the end of the decimal part should be removed to simplify the decimal; When the number of decimal places is not enough, use 0 to occupy the place.
3. Rule: the product of a number multiplied by 1 other than 0 is greater than the original number; The product of a number 0 divided by a number less than 1 is less than the original number.
4. There are usually three ways to find the approximate value:
(1) rounding method; (2) into law; (3) Tailing method
5. Calculate the amount of money, and keep two decimal places, indicating that the calculation has reached the point. Keep one decimal place, indicating that the angle has been calculated.
6. The order of four decimal operations is the same as that of integers.
7, operation law and nature:
Addition: additive commutative law: a+b=b+a
Additive associative law: a+b A+B+C = A+B+C b+c.
Multiplication: multiplication commutative law: a× b = b× a.
The law of multiplicative association: a×b×c = a×b×c 4 or 0.4 see 2.5, 8 or 0.8 see 1.25.
Multiplication and distribution law: when a+b×c=a×c+b×c or a×c+b×c=a+b×cb= 1, b is omitted.
Variants: a-b×c=a×c-b×c or a× c-b× c = a-b× c.
Subtraction: Subtraction property: A-B-C = A-B+C.
Division: nature of division: A ÷ B ÷ C = A ÷ B× C
Orientation of the Fifth Grade Mathematics Review Materials of People's Education Press
8. In order to determine the position of the object, it is necessary to use several pairs of first columns: vertical and horizontal. Two problems can be solved by using number pairs: one is to give a number pair and mark the point where the object is on the way to coordinate. The second is to give a point in the coordinates, which can be expressed by several pairs.
Decimal division
10, the meaning of fractional division: know the product of two factors and one of them, and find the operation of the other factor. For example, 0.6÷0.3 means that the product of two known factors is 0.6, one factor is 0.3, and what is the other factor?
1 1. Calculation method of decimal divided by integer: decimal divided by integer, divided by integer to divide. The decimal point of quotient should be aligned with the decimal point of dividend. The integer part is not divided enough, quotient 0, decimal point. If there is a remainder, add 0 and divide it.
165438+
Note: If there are not enough digits in the dividend, make up the dividend with 0 at the end.
12. In practical application, the quotient obtained by fractional division can also be rounded to a certain number of decimal places as needed to obtain the approximate number of quotients.
13, the change law of division: ① the quotient is unchanged: the dividend and divisor expand or contract by the same multiple at the same time, and the quotient is unchanged except 0. (2) The divisor is constant, the dividend expands and contracts, and the quotient decreases with the expansion. (3) The divisor is constant, the divisor decreases, but the quotient expands; The dividend is constant, the divisor is enlarged, but the quotient is reduced.
14, P28 Cyclic decimal: the decimal part of a number. Starting from a certain number, one number or several numbers appear repeatedly in turn. Such decimals are called cyclic decimals. Cycle segment: the decimal part of the cycle decimal, which is a number that appears repeatedly in turn. For example, pi of 6.3232 ... is 32. Abbreviation 6.32.
15, the number of digits in the decimal part is a finite decimal, which is called a finite decimal. The number of digits in the decimal part is infinite decimal, which is called infinite decimal. Decimals are divided into finite decimal and infinite decimal.
Possibility of reviewing materials for fifth-grade mathematics in People's Education Press.
16. There are three situations when the incident occurs: possible, impossible and certain.
17, possible events, probability. Taking the number of copies of several possible situations as the denominator and the single possibility as the numerator, we can find out the possibility of the corresponding event.