Extract common factor
In fact, this method uses multiplication, division and distribution to extract the same factor. If the remaining items in the exam are often added or subtracted, an integer will appear. Pay attention to the extraction of the same factor.
Borrowing method
When using this method, we need to pay attention to observation and find the law. Also pay attention to paying back the money. If you borrow it, it is not difficult to borrow it again.
When we see that an integer like 998,999 or 1.98 is close to a very easy calculation, we often use the borrowing method.
Split method
As the name implies, the splitting method is to split a number into several numbers for the convenience of calculation. This requires mastering some "good friends", such as 2 and 5, 4 and 5, 2 and 2.5, 4 and 2.5, 8 and 1.25. Be careful not to change the size of the number when splitting.
associative law of addition
Pay attention to the application of additive associative law (a+b)+c=a+(b+c), and get simpler operation by changing the position of addend.
Split method and multiplication distribution law
This method needs to master the distribution rules of division and multiplication flexibly. When you see that 99, 10 1 9.8 is close to an integer, you should first consider division.
Use reference number
Find a more eclectic number from a series of numbers to represent this series. Of course, remember that the selection of this number should not deviate too far from this series.
Using formula method
(1) addition:
Commutative law, a+b=b+a,
Law of association, (a+b)+c=a+(b+c).
(2) The nature of subtraction:
a-(b+c)=a-b-c，
a-(b-c)=a-b+c，
a-b-c=a-c-b，
(a+b)-c=a-c+b=b-c+a。
(3) Multiplication (similar to addition):
Commutative law, a*b=b*a,
Law of association, (a*b)*c=a*(b*c),
Distribution rate, (a+b)xc=ac+bc,
(a-b)*c=ac-bc。 (4) The nature of division operation (similar to subtraction):
a \(b * c)= a \b \c，
a \(b \c)= a \bxc，
a \b \c = a \c \b，
(a+b)÷c=a÷c+b÷c，
(a-b)÷c=a÷c-b÷c
Many previous algorithms and property formulas are changed by removing or adding brackets. Its rule is that in the same level of operation, parentheses are added or removed after the plus sign or multiplication sign, and the operation sign of the following value remains unchanged.
Add or remove parentheses after the minus sign or the division sign, and the operation sign of the following value will be changed.