Grades, Numbers and Counting Units (tables are important) distinguish between counting units and numbers.
How to read large numbers (the key is how to read zeros)
How to write large numbers
Expand the number to three orders of magnitude
2. Rounding method
It is estimated that two digits are rounded to the nearest ten, three digits to the nearest hundred and four digits to the nearest thousand. I guess I saw the calculation symbol clearly. Especially similar to 1500-500/50, some people will calculate the subtraction first.
Rounding method
The application problems involved here include the method of ending and the method of entering one.
10 people take a car, and every four people have a car. How many cars does a * * * need? Furthermore, the remaining two people need a car.
60 kilograms of water per barrel, how many barrels of water can a truck with a load of 2 tons hold at most? Tailing method, the remaining 20 kilograms can't hold a bucket of 60 kilograms of water.
3. Area unit
Square kilometer (square kilometer), square meter, square decimeter, square centimeter, square millimeter.
Combined length unit
Check perimeter and area
It is necessary to combine the reality and let the children have an idea of the basic length and area.
4. Unit right
Grams, kilograms and tons
5. unit of volume
ML, liter
The difficulty of this chapter lies in: realizing the quantity and conversion of quantity units in combination with reality.
Units should be unified
Perimeter and area
In fact, the most important thing is to determine the length and width (a square is the side length)
1, rectangle
Area = length * width
Perimeter =2* (length+width)
We already know the area and length (or width) and find the perimeter or the other side.
Length = area: width
(width = area/length)
Perimeter =2 (length+area/length) =2 (width+area/width)
We already know the length (or width) of a week. Find the area or the other side.
Length = circumference /2- width
Width = circumference /2- length
Area = length * (circumference /2- length)
= width * (circumference /2 times width)
2. Square
Area = square of side length
Perimeter =4* side length
Side length = area root (the square number that appears now is generally small, which can be calculated by multiplication formula table)
Side length = perimeter /4
Unit of length and unit of area
1 km =1000m
1M = 10DM = 100cm
1DM= 10CM
1 cm =10mm
1 km2 = 1 km2 = 1000000 m2
1 m2 = 100 square decimeter = 10000 square centimeter = 100000 square millimeter.
When the sum of two numbers is constant, when the difference is minimum or equal, the product is maximum.
That is to say, rectangles and squares with equal perimeters have the largest area (the smaller the length-width difference of rectangles, the larger the area). When the product of two numbers is constant, the difference is the largest and the sum is the largest.