What are the contents of mathematics in the second semester of "Children of Grade Three" by Shanghai Education Press? What about the first unit? Let's get to know it together!
Operation at the same level: symbols are all operations of addition, subtraction, multiplication and division, from left to right.
? Two-level operation: symbols have both addition and subtraction and multiplication and division, multiplication and division first and then addition and subtraction.
Attention, attention, attention.
1. The same level operation can be skillfully calculated.
For example, 230×46÷23 is calculated skillfully: 230×46÷23=230÷23×46.
2. Two-stage operation can't be calculated skillfully, but only in the order of operation. For example, 66+34×250 cannot be skillfully calculated.
Remember the order of operation in brackets: first calculate inside brackets, then calculate outside brackets.
When calculating skillfully, you can add parentheses.
It is preceded by a plus sign, followed by brackets and the same symbol.
Such as: 331+77+623 = 331+(77+623)
The MINUS sign is in front, followed by brackets, and the symbol should be changed.
For example:1324-177-223 = 2324-(177+223)
When moving the position: the symbol should move with the following numbers.
The operation order of recursive equation is: first calculate parentheses, then multiply and divide, and finally add and subtract.
In the face of irregular figures, we can also calculate their areas: generally, we use the square of 1 cm to count, and if it is less than a square, we will use the principle of "using 1 square for more than half a square, and discarding for less than half a square".
Finally, the area of irregular graphics is the number of full grids plus the number of semi-grids greater than or equal to.
1. A square with a side length of 1 decimeter and an area of 1 square decimeter can also be written as 1dm2.
4. Conversion between units
Senior unit (larger unit) → lower unit (smaller unit)? Progress rate
For example: 10 square decimeter =( 1000) square centimeter.
The calculation is as follows:10×100 =1000.
Lower unit (smaller unit) → higher unit (larger unit) divided by forward speed.
Such as: 800 square decimeter =( 8) square meters
The calculation is as follows: 800100 = 8.
By using the cut-and-fill method, the area problem of combined graphics is transformed into the problem of finding the sum or difference of several rectangles or squares.
When calculating the area of the combined graph, we should pay attention to:
1. Choose division or complement according to the diagram, and draw a dotted line with a ruler.
2. Calculate the length of the graphic edge related to this area and use the length unit.
3. Calculate the area, and then add and subtract.
Third grade children, come on! Every progress you make is our pride!