1,100000 is (one hundred thousand); 100000 is (one million); 101 million is (ten million); 1 010 million is (1100 million). The advance rate between every two adjacent counting units is 10. This counting method is called decimal counting method.
One, ten, one hundred, one thousand and one million are all counting units.
The position occupied by a counting unit is called a number. For example, one, ten, one hundred, one thousand, ten thousand ... are all numbers.
3. 1.2.3.4 ... represents the number of all objects (natural number). There is no object, which is represented by 0, and 0 is also a natural number.
4. The minimum natural number is (0), there is no maximum natural number, and the number of natural numbers is (infinite).
5. Comparison of numbers: first grade, then count, the number with more digits will be larger; The digits are the same. Compared with the highest bit, the number of the highest bit is larger. If the highest digit is the same, compare the next digit.
6. How to read numbers above 100 million: first grade, and then read from a high position. After reading the figures of 100 million or 10 thousand, add the words "100 million" or "10 thousand" There is a zero or several zeros in the middle of each level, and all of them are read only "zero", and the zeros at the end of each level are not read.
7. Rewrite and find out the approximate figures.
(1) Rewrite the integer of ten thousand (or one hundred million) into a number with the unit of ten thousand (or one hundred million), remove the four zeros (or eight zeros) at the end and add the word ten thousand (or one hundred million).
(2) If a number that is not 10000 (or an integer of 10000 million) is rewritten as a number with "10000" (or "10000 million") as the unit, "/kloc-0"
? Unit 2? Hectares and square kilometers
9. The area of land can be measured in "hectares".
The measurement of relatively large land area is usually based on "square kilometers".
The square with a side length of 100 meters has an area of 1 hectare.
1 ha = 1 10,000 m2
A square with a side length of 1 km and an area of 1 km2.
1km2 =1million m2 = 100 hectares.
Unit 3? Angle measurement
10, the light emitted by flashlights, car lights and the sun can be approximately regarded as rays. A ray has only one endpoint and can extend to one end indefinitely.
1 1. A straight line has no end points and can extend to both ends indefinitely, and its length cannot be measured;
The ray has 1 endpoints, which can extend to one end indefinitely, and the length cannot be measured;
A line segment has two endpoints, which cannot be extended indefinitely, and its length can be measured.
12, countless straight lines can be drawn after one o'clock, and only one straight line can be drawn after two o'clock.
When drawing a straight line, both sides should stand out, otherwise it will be drawn as a line segment.
13, the figure composed of two rays drawn from a point is called an angle.
14, measure the angle with a protractor. The unit of measurement of an angle is "degree", which is represented by the symbol "degree".
Divide the semicircle into 180 equal parts, and the angle of each part is 1 degree, and record it as 1 degree.
15, steps of measuring angle:
(1) The center of the protractor coincides with the vertex of the angle, and the 0 scale line coincides with one side of the angle;
(2) Look at the scale on the protractor on the other side of the angle, which is the degree of this angle.
16, the size of the angle has nothing to do with the length drawn on both sides of the angle. The size of the angle depends on the size of both sides. The bigger the fork, the bigger the angle. Observing under a magnifying glass, the angle will not change.
17, acute angle < 90, right angle = 90,9096,
You don't need to bring a unit, but you should pay attention to the comparison with the same unit.
Example 2: Xiaojun's home is 420 meters away from school. Xiaojun walks an average of 62 meters per minute when he goes to school. Can he walk to school in six minutes?
At first glance, 62 is not an integer ten. Of course, we won't use division. It is easiest to use the multiplication we have learned:
Solution: 62×6=372 (meters) 372 < 420 A: He can't walk to school in six minutes.
4. The speed unit is usually the test center:
Example: Uncle drove from A to B. It took him five hours to go there at 60 kilometers per hour, and two hours less when he came back. What is the average speed when he comes back?
Solution: ① Find the average speed, speed = distance/time.
First, calculate the distance between the two places, that is, the distance when going, and the distance when coming back is 60× 5 = 300 (km).
Then calculate the time for your return 5-2 = 3 (hours).
Finally, calculate the speed when you come back. Note that the speed unit is 300 ÷ 3 = 100 (km/h).
5. Skills of multiple questions
Example: Four boxes of bees can brew 300 kilograms of honey a year. Kobayashi keeps 12 boxes of such bees. How many Jin of honey can he brew a year?
Option 1: You can first calculate how much honey each box of bees can brew a year.
(that is, find the quantity of 1 multiplied by 300 ÷ 4 = 75 (kg).
/kloc-how much honey can a 0/2 box of bees brew a year? 75× 12 = 900 (kg).
Solution 2: You can also calculate how many times 12 box is 4 boxes 12 ÷ 4 = 3 (multiples need not be written as a unit).
Then the honey that bees can brew in the same time is 300× 3 = 900 (kg).
6, the best solution (with the same money to buy the most goods)
Solution: First look at which scheme is better, try to buy it with this scheme, and finally consider other schemes if there is surplus.
Example: Shopping malls sell shirts, one in 29 yuan and two in 49 yuan. The teacher has 185 yuan. How many shirts can I buy at most? How much money is left?
Solution: Comparing the two schemes, "two pieces of 49 yuan" is cheaper (as long as one piece doesn't arrive in 25 yuan), so try to buy it by "two pieces at 49" first, and you can buy three sets (***6 pieces). The formula is 185 ÷ 49 = 3 (sets) ... 38 (yuan), 2. So in the end, you can buy 7 yuan and the remaining 9 yuan.