The meaning of multiplying decimal by decimal is to find a fraction of this number. For example, 2.6×0.4 is four tenths of 2.4. What is it? What is 8.5×3.4 times that of 8.5?
2. Calculation method of decimal multiplication: To calculate decimal multiplication, first calculate the product by integer multiplication, then look at a factor * * * and how many decimal places there are, count the digits on the right side of the product and point to the decimal point; When the number of decimal places of the product is not enough, 0 should be added in front, and then the decimal point should be calculated; Those with zeros after the decimal point should be removed.
3. A number (except 0) multiplied by a number greater than 1 is greater than the original number, and a number (except 0) multiplied by a number less than 1 is less than the original number.
3.' The order of four decimal operations is the same as that of integers': the first number with brackets, the first number without brackets, multiplication and division, addition and subtraction, and the same-level operations are calculated from left to right.
4. The commutative law, associative law and distributive law of integer multiplication are also applicable to fractional multiplication.
Knowledge points 2 1, decimal multiplication integer: meaning-a simple operation to find the sum of several identical addenda in mathematics of Jiangsu Education Edition.
For example, 1.5×3 indicates how many times 1.5 is or the sum of three 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.
2. Decimal multiplied by decimal: meaning-that is, what is the fraction of this number.
For example, 1.5×0.8 is to find what is eight tenths of 1.5.
How much is 1.5× 1.8? It is 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 (1): a number (except 0) is multiplied by a number greater than 1, and the product is greater than the original number;
A number (except 0) is multiplied by a number less than 1, and the product 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 is completed. 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 Addition Law: (a+b)+c=a+(b+c).
Subtraction: Subtraction property: A-B-C = A-(B+C) A-(B-C) = A-B+C.
Multiplication: multiplicative commutative law: a×b=b×a multiplicative associative law: (a×b)×c=a×(b×c) multiplicative distributive law: (a+b )× c = a× c+b× c (a-b )× c = a× c-b× c.
Division: nature of division: a÷b÷c=a÷(b×c)