Quick calculation skills in grades one and two, children in grades one and two generally need to calculate addition and subtraction when learning mathematics, and there are certain skills in quick calculation, which we need to master. Here are some quick calculation skills for the first and second grades.

Fast calculation skills of senior one and senior two: 65438+ zero addition simple calculation method

No matter how much you add, the most basic principle is the addition principle within 20. The fast formula of carry addition within 20 is: add 90% minus one, add 80% minus two, add 70% minus three, and add 60% minus four. Because addition has commutative law, we only need to remember these words. In addition, within 100, first observe the two digits, find out the larger one, and get the answer quickly according to the formula calculation.

Round-up priority algorithm

Example 1.24+44+56

=24+(44+56)

=24+ 100= 124

Solution: Because 44+56= 100 is an integer, it is easier to calculate their sum first, and then add other numbers.

Example 2.53+36+47

=(53+47)+36

= 100+36= 136

Solution: Because 53+47= 100 is an integer, move the symbols before +47 and +36 together and then calculate the sum of 53+47.

Develop a good habit of calculation.

Developing good computing habits is an effective way to improve children's computing ability. Help children develop the following good calculation habits, and do the serious calculation habits of "seeing, thinking and calculating".

Calculation is a very serious matter, and we can't be careless, but just some children don't have good study habits. After getting the calculation problem, they can't see the numbers clearly, and they can't see the operation order clearly, so they calculate blindly.

Fast calculation skills in grades one and two 2 additive commutative law's law of sum and addition

Additive commutative law;

When two numbers are added, the positions of addends are exchanged, and their sum remains the same. That is, a+b = b+a.

Generally speaking, when multiple numbers are added, the order of addition is arbitrary and the sum is constant.

a+b+c+d=d+b+a+c

Additive associative law:

Add a few numbers, first add the first two numbers, then add the third number; Or, add the last two numbers first, and then add them to the first number, and their sum remains the same. Namely: a+b+c = (a+b)+c = a+(b+c),

Three basic ideas commonly used in quick calculation and clever calculation

1. Round (target: one hundred thousand yuan only ...)

2. Divide it (after dividing it, you can make ten thousand ...)

3. Combination (reasonable grouping and reorganization)

Three common methods

Rounding method

When two numbers are added, if they can just be added to whole ten, whole hundred, whole thousand and whole ten thousand, one of them is called the "complement" of the other number. Using the "complement" to calculate the addition skillfully is usually called "rounding method".

For example,1+9 =10,3+7 =10,2+8 =10,4+6 =10,5+5 =10.

Another example: 1 1+89= 100, 33+67 = 100, 22+78= 100, 44+56= 100.

In the above formula, 1 is called the "complement" of 9; 89 is called the "complement" of 1 1, and1is also called the "complement" of 89. In other words, two numbers are complementary to each other.

For a large number, how to quickly calculate its "complement"? Generally speaking, you can "round up" numbers by adding all the numbers from the most significant bit to get 9, and then adding the last digit to get 10.

Such as: 87655→ 12345, 46802→53 198, 87362→ 12638, …

Let's talk about the clever use of "complement" to calculate addition, which is commonly called "rounding method"

Skillfully calculate the following questions:

①36+87+64

②99+ 136+ 10 1

③ 136 1+972+639+28

Solution:

① Formula = (36+64)+87 =100+87 =187.

② formula = (99+101)+136 = 200+136 = 336.

③ Formula = (1361+639)+(972+28) = 2000+1000 = 3000.

Combined rounding method

(1) When removing brackets, if there is a "+"before the brackets, the operation sign of the numbers in the brackets will remain unchanged after removing the brackets; If there is a "-"in front of the parentheses, after removing the parentheses, the operation symbol "+"of the number in parentheses becomes "-"and "-"becomes "+".

(2) In addition and subtraction mixed operation, when adding brackets: if there is a "+"sign in front of the brackets, the original operation sign of the numbers in brackets remains unchanged; If you add parentheses before a symbol "-",the original operator "+"of the number in parentheses will become "-"and "-"will become "+".

(3) Before the operation, use "complement" to round up the numbers close to integer ten, integer hundred, integer thousand, etc. (pay attention to subtracting redundant numbers and adding redundant numbers).

Benchmark method

In the process of subtraction, using the principle of complement, several subtractions are rounded up first and then subtracted. When using the benchmark number method, we should choose the number with small difference from each number as the benchmark number, which is convenient for calculating the cumulative difference. At the same time, considering that the product of reference number and addend can be easily calculated, the selection of reference number should be as reasonable as possible.

Fast calculation skills of senior one and senior two 3. Simple calculation of three-character classics

The simple calculation is enjoyment. Observe carefully and find the features.

Keep adding and knotting pairs. Ride in a row and find friends.

Continuous subtraction, subtraction, addition. Continuous division, by product.

Subtract sum, and you can even subtract it. Divide by the product, you can divide by it.

Multiply and difference, multiply separately. Add and subtract, don't panic,

The same factor, put forward, different factors, put in brackets.

At the same level, interchangeable. Special number, cleverly split.

Reasonable, I can do it.

Seven common simple operation methods

Method 1: signed moving method

When a calculation problem only has the same level operation (only multiplication and division or only addition and subtraction) without brackets, we can "move with signs"

a+b+c=a+c+b

a+b-c=a-c+b

a-b+c=a+c-b

a-b-c=a-c-b

a×b×c=a×c×b

a \b \c = a \c \b

a×b÷c=a÷c×b

a \b×c = a×c \b

Method 2: Constraint method

(A) bracket method

1. When adding parentheses, there is a plus sign in front of the parentheses, a constant sign in the parentheses, a minus sign in front of the parentheses, and a sign in the parentheses.

2. When the multiplication and division method is bracketed, the multiplication symbol is in front of the bracket, the constant symbol is in the bracket, the division symbol is in front of the bracket, and the symbol is changed in the bracket.

(2) Method of removing brackets

1. In addition and subtraction, when removing brackets, add a plus sign and a minus sign before the brackets. When the brackets are removed, the symbol will be changed (the original addition in brackets is now reduced; It used to be negative, but now it is positive. )。

2. When removing the brackets in the multiplication and division method, add a multiplication sign in front of the brackets, a constant sign after the brackets, and a division sign after the brackets (the multiplication in the original brackets is now divided; It used to be division, but now it's multiplication. )。

Method 3: Multiplication and distribution law

1. allocation method

Parentheses are addition or subtraction operations, multiplied by another number. Pay attention to distribution.

Example: 8×(3+7)

=8×3+8×7

=24+56

=80

Step 2: Extract common factors.

Pay attention to the extraction of the same factor.

Example: 9×8+9×2

=9×(8+2)

=9× 10

=90

3. Pay attention to the structure to make the formula conform to the conditions of multiplication and division.

Example: 8×99

=8×( 100- 1)

=8× 100-8× 1

=800-8

=792

Method 4: Rounding method

See the name, and you will know the meaning of this 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.

For example: 9999+999+99+9

=( 10000- 1)+( 1000- 1)+( 100- 1)+( 10- 1)

=( 10000+ 1000+ 100+ 10)-4

= 1 1 1 10-4

= 1 1 106

Method 5: Split method

Split 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, 4 and 25, 8 and 125. Be careful not to change the size of the number when splitting.

For example: 32× 125×25

=4×8× 125×25

=(4×25)×(8× 125)

= 100× 1000

= 100000

Method 6: change division into multiplication skillfully

Dividing by a number is equal to multiplying the reciprocal of this number.

Method 7: Split terminology method

Fractional splitting refers to splitting the items in the fractional formula so that the split items can be offset before and after. This split item calculation is called split item method. The common splitting method is to split a number into the sum or difference of two or more digital units.

When you encounter the calculation problem of cracked items, you should pay attention to:

1. continuity

2. Homomorphism

Calculation method: head and tail reduction. In addition to tolerance.