Operation law, nature and content
Add with letters.
Additive commutative law's arithmetic law is that when two numbers are added, the positions of addends are exchanged, and their sum remains unchanged.
a+b=b+a
The law of addition and association adds three numbers, first the first two numbers, then the third number; Or add the last two numbers first, and then add the first number, and their sum remains the same.
(a+b)+c=a+(b+c)
increase
Algorithm Multiplication method of substitution Multiplies two numbers, and the position of the exchange factor is the same. A×b=b×a Multiplication Association Law Multiply three numbers, first multiply the first two numbers and then multiply the third number.
Multiplication; Or multiply the last two numbers first, and then multiply them with the first number, and their products remain unchanged.
(a×b)×c=a×(b×c)
Multiplication and Distribution Law When the sum of two numbers is multiplied by a number, the two addends can be divided separately.
Multiply this number and add the two products.
(a+b)×c=a×c+b×c quotient invariance law
In division, the divisor and divisor expand or shrink at the same time by the same multiple (except zero), and the quotient remains unchanged. The nature of division A number divided by two numbers can be divided by the product of these two numbers.
You can also divide by the first divisor and then divide by the second divisor. a÷b÷c=a÷(b×c)
Subtraction attribute
If you subtract several numbers from a number in succession, you can subtract the sum of all subtractions from this number, and the difference remains the same.
a-b-c=a-(b+c)
Some simple techniques
A, borrow it skillfully, but pay attention. If you borrow it and return it, it is not difficult to borrow it again.
9999+999+99+9 482 1-998
B, split, don't change the size of the number.
3.2× 12.5×25 1.25×88 3.6×0.25
C, skillfully change the division into multiplication (divided by 4 1 is equivalent to multiplying by 4 and then dividing by 8 1.
Equivalent to multiplying by 8, ...)
7.6÷0.25 3.5÷0. 125 =7.6÷4
1 =7.6×4
D, pay attention to the structure, so that our formula meets the conditions of multiplication and division and distribution.
1.8×99+ 1.8 3.8×9.9+0.38
257× 103-257×2-25