1.MM: It is a unit of length and rainfall, abbreviated as mm in English.
1mm = 0. 1cm；
=0.0 1 decimeter;
= 0.00 1m；
=0.00000 1 km
2. centimeter: it is a unit of length measurement, equal to one hundredth of one meter. Unit of length, symbol: cm. ， 1cm = 1/ 100m。
1 cm = 10/0mm
=0. 1 decimeter
=0.0 1 m
=0.0000 1 km.
3. decimeter: it is one of the metric units of length, and 1 decimeter is equivalent to one tenth of 1 meter.
0.000 1 km = 1 decimeter
0. 1 meter (m) = 1 decimeter
10cm = 1 decimeter
100 mm = 1 decimeter
10 decimeter = 1 meter (meter)
0. 1 decimeter = 1 cm
0.0 1 decimeter = 1 millimeter (mm)
4. Kilometers: Kilometers, also called kilometers, are units of length and are usually used to measure the distance between two places. It is the international standard unit of length measurement, and the symbol is km.
1 km (km) = 1 0,000m (m) =100,000m (cm) = 1 0,000mm (mm)
5. Ton: mass unit. In the metric system, one ton is equal to 1000 kg.
6. Addition: one of the four basic operations, which refers to the calculation of combining two or more numbers and quantities into one number and quantity. Yes. The addition symbol is the plus sign (+). Connect items with a plus sign when adding. Put and after the equal sign (=). Example: If the sum of 1, 2 and 3 is 6, it is written as 1+2+3 = 6.
7. Add the name of each part.
"+"is a plus sign, the numbers before and after the plus sign are addends, "=" is an equal sign, and the numbers after the equal sign are sums.
100 (addend)+(plus sign) 300 (addend) = (equal sign) 400 (sum)
8. Additional nature
(1) additive commutative law: a+b = b+a.
(2) Additive associative law: a+b+c=a+(b+c)
9. subtraction: it is one of the four operations. The operation of subtracting one number or quantity from another is called subtraction.
Given the sum of two addends and one of them, the operation of finding the other addend is called subtraction.
10. the essence of subtraction: subtracting a number is equal to adding the reciprocal of this number.
1 1. Check calculation: After calculating the problem, do it again with inverse operations (such as subtraction, addition, subtraction, multiplication and division, multiplication) to check whether the results of the previous operations are correct.
12. The function of check calculation: check calculation can effectively detect errors in the calculation process, but it is not very useful for solving errors. By comparing the data obtained by checking calculation (using the results to derive conditions) with the original data, it is suggested whether the operation is correct.
13. quadrilateral: a closed three-dimensional figure surrounded by four line segments that are not on the same line is called quadrilateral. It consists of convex quadrilateral and concave quadrilateral.
14. Parallelogram: Two groups of parallelograms with opposite sides are called parallelograms.
15. Perimeter: The integral of the perimeter of the edge of a finite area is called perimeter, and the length of the graph is the perimeter of the graph. Therefore, the perimeter is equal to the sum of all the edges of the graph.
16. estimate: roughly infer the nature, quantity and change of things according to the situation.
17. Remainder: In the division of integers, there are only two situations: divisible and non-divisible. When it is not divisible, a remainder is generated, and the remainder operation is: 1 It refers to the undivided part of the dividend in integer division.
For example, if 27 is divided by 6, the quotient is 4 and the remainder is 3.
18. Properties of remainder: The remainder has the following important properties (A, B and C are all natural numbers):
(1) The remainder is less than the divisor.
(2) Dividend = divisor × quotient+remainder;
Divider = (dividend-remainder) ÷ quotient;
Quotient = (dividend-remainder) divider;
Remainder = dividend-divisor × quotient.
19.second: Time unit Time unit second is the basic unit of time in the international system of units, and the symbol is S.
20. Minute: Time unit, equal to 1/60 hours or 60 seconds.
2 1. multiplication: refers to a shortcut to add the same numbers. The result of the operation is called product.
22. The name of each number in the multiplication formula
"×" is a multiplication sign, the numbers before and after the multiplication sign are called factors, "=" is an equal sign, and the numbers after the equal sign are called products.
10 (factor) × (symbol) 200 (factor) = (symbol) 2000 (product)
23. Score:
Divide the unit "1" into several parts on average, and the number representing such a part or parts is called a fraction. The number representing this share is called the fractional unit.
The numerator is above the denominator, which can also be regarded as division. The numerator is divided by the denominator, and the opposite multiplication can also be expressed as a fraction.
24. Fraction line, numerator and denominator
The horizontal line in the middle of the score is called fractional line, the number above the fractional line is called numerator, and the number below the fractional line is called denominator. Read it as a score.
Fractions can be expressed by the division formula: for example, half equals 1 divided by 2. Where 1 numerator is equal to dividend,-fractional line is equal to divisor, denominator of 2 is equal to divisor, and 0.5 fractional value is equal to quotient.
25. Source of scores
Fractions have a long history in China, and the original forms of fractions are different from the present ones. Later, India appeared a score representative similar to China's. Later, the Arabs invented the fractional line, and the expression of the score became like this.
More than 200 years ago, the Swiss mathematician Euler said in his book General Arithmetic that it is impossible to divide a 7-meter-long rope into three equal parts because there is no suitable number to represent it. If we divide it into three equal parts, each part is 7/3 meters. Like 7/3 is a new number, which we call a fraction.
26. Possibility: Possibility refers to the probability of things happening, which is a quantitative indicator contained in things and indicates the development trend of things.
The above are the knowledge points of mathematics in the third grade of primary school, I hope it will help you.