Tisch
Knowledge points of key units of mathematics in the third grade of primary school (1) test 1. In life, a small number of items can be used in units (millimeters, centimeters, decimeters); Large objects are usually measured in meters; Generally, the unit for measuring long distances is (km), also called (km).
2. There are (10) units in the length of 1 cm, and the length of each unit (equal) is (1) mm. ..
3. 1 The thickness of coins, rulers, magnetic cards, buttons and keys 1 min is about1mm..
4. When calculating the length, you can only add or subtract the same length unit.
Tip: When converting the length unit, change the large unit to the small unit and add 0 at the end of the number (if there are several 0s in the relationship, add several 0s); Changing a small unit to a large unit will remove the zeros at the end of the number (if there are several zeros in the relationship, remove several zeros).
5. The relationship between length units is as follows: (the propulsion rate between every two adjacent length units is 10).
① the advancing rate is 10: 1 m = 10 decimeter, 1 decimeter = 10 cm, 10 mm,10 mm.
② The advancing speed is 1 00:1m =100 cm,1decimeter = 100 mm, 100 cm = 1 m,/kloc-0.
③ The forward speed is1000:1km =1000 m,1km = 1000m = 1km.
extreme
The key unit of mathematics in the third grade of primary school (2) quadrilateral 1, which has four straight sides and four closed angles, is called quadrilateral.
2. Features of quadrilateral: It has four straight sides and four corners.
3, the characteristics of the rectangle: the rectangle has two lengths and two widths, the four corners are right angles, and the opposite sides are equal.
4. Characteristics of a square: it has four right angles and four equal sides.
5. Rectangular and square are special parallelograms.
6, the characteristics of parallelogram:
(1) The opposite sides are equal and the diagonal lines are equal.
② Parallelogram is easy to deform. (Triangle is not easy to deform)
7. The length of a closed graph is its perimeter.
8. Formula: The circumference of a rectangle = (length+width) ×2 or length ×2+ width ×2.
Length of rectangle = perimeter ÷2- width
Width of rectangle = perimeter ÷2- length
Circumference of a square = side length ×4
Side length of a square = perimeter ÷4,
Tisso
Knowledge points of key units of mathematics in the third grade of primary school (3) 1. When we express the weight of an object, we usually use (mass unit). In life, the weight of lighter items can be measured in grams. According to the quality of general goods, it is usually a unit (kg); Measure the mass of heavy or bulk goods, usually in tons.
Tip: in the conversion of "ton" and "kilogram", converting tons into kilograms means adding three zeros at the end of the number; Converting kilograms into tons is to remove the three zeros at the end of the number.
2. The ratio of two adjacent mass units is 1000.
1 ton = 1000 kg
1 kg =1000g
Addition and subtraction within 10 thousand
1, know the integer thousand (memory: 10 thousand is ten thousand)
2. Read and write numbers (write Chinese characters when reading and Arabic numerals when writing numbers).
No matter whether there is a zero or several zeros at the end of a number, this zero will not be read.
② There is a zero or two consecutive zeros in the middle of a number, and both of them read only one zero.
3. Comparison of figures:
① Numbers with different digits are larger, and those with more digits are larger.
(2) Compare the sizes of numbers with the same number of digits. First, compare the numbers on the numbers of these two numbers. If two digits are the same, compare the next digit, and so on.
4. Find the approximate value of a number: Memory: Look at the last digit. If it is 0-4, use the four-shed method. If it's 5-9, use the decimal method. The digits and minimum digits of 5 are 9, and the minimum digits are 0. The second digit is 99, the smallest digit is 10, the third digit is 999, the smallest third digit is 100, the fourth digit is 9999, the smallest fourth digit is 1000, the fifth digit is 9999, and the smallest fifth digit is 65999.
6, the minuend is a three-digit continuous abdication subtraction operation steps:
① When the columns are vertical, the same numbers must be aligned;
(2) When subtracting, which digit is not reduced enough, subtract 1 from the last digit and add10 to the standard; If the previous digit is 0, it is 1 of the previous digit.
7. Pay attention to the middle 0 when doing the problem, because it is abdicated continuously, so you should retreat from one hundred to ten at 10, and then from ten to one at 10, and lend one, so there are only nine left in the ten, not 10. (Sum of two three digits: it may be three digits or four digits. )
8. Formula: minuend = subtraction+difference
Sum = Addendum+Another Addendum
Subtraction = minuend-difference
Appendix = Sum-Another Addendum
Difference = minuend-minuend