Quick arithmetic formulas within 100, mental arithmetic skills within 100

The ring finger is a "3" and the little finger is extended to "4";

Hold the thumb with four fingers, and remember that the thumb is "5";

Extend your index finger to your little finger again, and "6", "7", "8", and "9" are numbered.

Practice the mantra with the fingers of the right hand.

One horse takes the lead, two tigers compete, three words and two words, the four seas are home, the five grains are abundant, the six animals are prosperous, seven up and eight down, eight immortals cross the sea, nine cows and one hair, 100,000 urgent.

One word and nine tripods, two dragons play with pearls, three-legged tripods, embattled, abundant grains, six gods without owners, seven up and eight down, eight sides exquisite, nine cows and one hair, perfect.

Note: When reading "100,000 urgent" or "perfect", the right hand is clenched into a fist, and the left hand is "1", which represents the carry position. ）

Practice the mantra with the fingers of the left hand.

ten, twenty, thirty, forty; Fifty, sixty, seventy, eighty, ninety, one hundred.

Note: When you say "one hundred", clap your hands with high-fives, then clench your fists in front of your chest. ）

Count with both hands.

Note: According to the cognitive level of children of each age, choose the size of the number. ）

Addition exercises. Note: When doing addition exercises, such as "3+5", the right hand comes out of "3" first, and the process of "5" is:

Say "add 1" in your mouth and give out your little thumb; Say "add 2" in your mouth, and stretch your thumb with four fingers (note that the thumb only represents "1" in the process of finger exit, and only when the number is fixed, the thumb is regarded as "5"); Say "add 3" in your mouth and take out your index finger; Say "add 4" in your mouth and take out your middle finger; Say "add 5" in your mouth and get your ring finger out. At this time, the fixed number begins, and only the little finger of the right hand is not opened, and the result is "8".

Addition formula table within 10.

Addition formulas within 20.

Addition formulas within 30.

Addition formulas within 40.

Addition formulas within 50.

Addition formulas within 60.

Addition formulas within 70.

Addition formulas within 80.

Addition formulas within 90.

Addition formulas within 100.

Platform Statement.

1. A dozen times a dozen. Formula: head by head, tail by tail, tail by tail.

Example: 12 14=? Solution:

1×1=1，2＋4＝6，2×4＝8，12×，14=168。Note: Multiply the single digits, and use 0 to occupy the place if the two digits are not enough.

2. The head is the same, and the tail is complementary (the sum of the tails is equal to 10). Formula: After adding 1 to a head, the head is multiplied by the head, and the tail is multiplied by the tail.

Example: 23 27=? Solution:

2＋1＝3，2×3＝6，3×7＝21，23×27=621。Note: Multiply the single digits, and use 0 to occupy the place if the two digits are not enough.

3. The first multiplier is complementary, and the other multiplier is the same. Formula: After adding 1 to a head, the head is multiplied by the head, and the tail is multiplied by the tail.

Example: 37 44=? Solution:

3+1=4,4 4=16,7 4=28,37 44=1628,Note: Multiply the single digits, and use 0 to occupy the place if the two digits are not enough.

Carry addition of two digits plus two digits:

Formula: add 9 to subtract 1, add 8 to subtract 2, add 7 to subtract 3, add 6 to subtract 4, add 5 to subtract 5, add 4 to subtract 6, add 3 to subtract 7, add 2 to subtract 8, add 1 to subtract 9. (Note: The number of additions in the oral decision is the number in the single digit).

Example: 26+38=64 Solution: Add 8 to subtract 2, who subtracts 2? 6 on 26 minus 3 on 10 to 4.

Note: How to carry the ten digits on the last two-digit number, is 1 I enter 2, is 2 I enter 3, is 3 I enter 4, and so on. So where to carry it, enter the second two-digit upper tenth.

If this time it is 3 and I enter 4, it is 2+4=6 in these two two-digit numbers. Here, 26 + 38 = 64 is 6-2 = 4 written in the single place, and 3 into 4 plus 2 is equal to 6 written in the ten place.

Another example is 42 + 29 = 71. Just use the sentence to add 9 to subtract 1, 2-1 = 1, write 1 in the single place, is 2 I into 3, 4 + 3 = 7, write 7 in the ten place to get 71.

The addition of two simple digits plus two digits without carrying, just write the number directly, such as 25 + 34 = 59, the single digit plus the single digit written in the single digit after the equal sign 5 + 4 = 9, ten digits plus ten digits written on the ten digits can be 2 + 3 = 5, that is, 59. There is no need to list the birds in this vertical calculation.

This method has been tried and tested.

Faster than a calculator.

The skills of oral arithmetic within 10 are as follows:

1. Addition. Remember the large number in mind, and the decimal number up the number, such as 4+2= Keep 4 in mind, count two numbers up, and then get the result 4+2=6.

2. Subtraction. Remember the large number in your heart, and count the small number down, e.g. 6-3 = Remember 6 in your heart, count down to three numbers, and then get the result 6-3 = 3.

1. Addition. Remember the large number in mind, and the decimal number up the number, such as 4+2= Keep 4 in mind, count two numbers up, and then get the result 4+2=6.

2. Subtraction. Remember the large number in your heart, and count the small number down, e.g. 6-3 = Remember 6 in your heart, count down to three numbers, and then get the result 6-3 = 3.

Oral arithmetic skills within ten,I personally think it's a way to make ten.,There's also a way to find friends.,Of course, I think the vertical up and down method of oral arithmetic,The key is to have a good brain to remember the flexibility of the brain.,So it will be more useful.。

Here are some tips for quick math questions:

1.If several numbers can be added to form a whole ten, you can change the position of the added number and add several numbers.

2.Use the subtraction property to "round" subtract several numbers from a number in a row, if the sum of the subtractions can be made up into a whole ten, you can add the subtractions first and then subtract them. This kind of oral arithmetic is relatively simple.

3.Near. Ten, nearly hundred, nearly a thousand numbers, counting God let Li calculate when he can close to the whole.

10. Whole hundred, whole thousand......The number of is considered as a whole.

10. Whole hundred, whole thousand......of the number of answers.

4.The complement method uses the "complement method" to add 1 to each addition for calculation.

5.Using the commutative law of addition and subtraction: the problem of adding first and then subtracting can also be made as subtracting first and then adding.

6.When calculating the number of integer hundreds, you can first look at the number in the problem as two parts: the whole number of hundreds and the "number of fractions", and then add and subtract the number of whole hundreds and the number of whole hundreds, and the number of "fractions" and "fractions" of the number of "fractions".

7.In the signed moving method, when a calculation problem has only the same level of operations (only multiplication and division or only addition and subtraction) and no parentheses, we can "move with signs".

8.Combined with the Law.

1) Bracketed method.

When adding parentheses to addition and subtraction operations, the parentheses are preceded by a plus sign, the parentheses are unchanged, the parentheses are preceded by a minus sign, and the parentheses are changed.

When adding parentheses to the multiplication and division operation, the parentheses are preceded by the multiplication sign, the parentheses are unchanged, the parentheses are preceded by the division sign, and the parentheses are changed by the sign.

2) De-bracket method.

When removing parentheses in addition and subtraction operations, the parentheses are preceded by the plus sign, the parentheses are removed and the parentheses are unchanged, and the parentheses are preceded by the minus sign, and the parentheses are removed to change the sign (the original addition in the parentheses is now to be subtracted; It used to be minus, but now it is going to be added).

When removing parentheses in the multiplication and division operation, the parentheses are preceded by the multiplication sign, the parentheses are removed and the invariant sign is removed, and the division sign is preceded by the parentheses. It used to be dividing, but now it is going to be multiplied. ）

8.Multiplication distributive law.

1) The parentheses of the distribution method are addition or subtraction operations, multiply with another number, pay attention to the distribution.

2) The extraction of common factors pays attention to the extraction of the same factor.

9.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, 4 and 25, 8 and 125, etc. Also be careful not to change the size of the slippery sock variable.

First of all, the same digits need to be aligned, single digit to single digit, ten digits to ten digits, the symbol (+ is written on the far left of the equation, aligned with the number of the second row, and the equal sign (=) is represented by a horizontal line. Vertical calculations, whether adding or subtracting, start from the single digit. When two digits are added, the single digit is full of ten, and 1 is advanced to the ten digit.

When the pen calculates the two-digit subtraction, the single digit is not enough to subtract, retract 1 from the ten digits, add 10 to the single digit and subtract again.

Note: The number on the bit is 0, be sure to mark it; But the number on the ten digit is 0 and does not need to be marked.

No matter how big the number is added, its most basic principle is the principle of addition within 20, and the quick calculation formula for carry addition within 20 is: add 9 to subtract 1, add 8 to subtract 2, add 7 to subtract 3, add 6 to subtract 4, add 5 to subtract 5, add 4 to subtract 6, add 3 to subtract 7, add 2 to subtract 8, add 1 to subtract 9 (note: the addition in the oral decision is to say the number in the single digit).

Since addition has a commutative law, we only need to remember these few sentences, in addition within 100, first observe the two digits, find out the larger number between them, and calculate according to the formula to quickly calculate the answer.

The abdication subtraction of numbers within 100 is also based on the abdication subtraction of numbers within 20, and the quick calculation formula of abdication subtraction is: subtract 9 to add 1, minus 8 to add 2, minus 7 to add 3, minus 6 to add 4, minus 5 to add 5, minus 4 to add 6, minus 3 to add 7, minus 2 to add 8, minus 1 to add 9 (note: the subtraction in the oral decision is to say the number on the single digit).

Since the subtraction and the subtraction cannot be exchanged, in subtraction, the two single digits are observed first, and when the subtraction is larger than the single digit of the subtracted number, the answer can be quickly calculated according to the subtraction formula.

1. The single digit is a quick calculation formula of "1": head multiplied by head, head plus head, tail is 1 (head plus head if more than 10 to be carried).

2. The ten-digit number is the quick calculation formula of "1": the head is 1, the tail is added, and the tail is multiplied by the tail (more than 10 to be carried).

3. The single digit is a quick calculation formula of "9": add 1 to each head, multiply and multiply by 10, subtract the additive, and finally put 1.

5. The head is the same, the tail complements (tail complementary: the mantissa is added to 10) Quick calculation formula: the head is multiplied by the head plus 1, and the tail is multiplied by the tail occupies 2 places.

6. The head complements each other, and the tail is the same quick calculation formula: the head is multiplied by the head and the tail, and the tail is multiplied by the tail to occupy 2 places.

7. The speed key gesture of the complementary number multiplied by the stacked number: the head plus 1 and then multiply the head, and the tail multiplies the tail by 2.

8. One of them is the quick calculation formula of 11: don't move from beginning to end, add and put in the middle.

1. A dozen times a dozen. Formula: head by head, tail by tail, tail by tail.

Example: 12 14=? Solution:

1×1=1，2＋4＝6，2×4＝8，12×，14=168。Note: Multiply the single digits, and use 0 to occupy the place if the two digits are not enough.

2. The head is the same, and the tail is complementary (the sum of the tails is equal to 10). Formula: After adding 1 to a head, the head is multiplied by the head, and the tail is multiplied by the tail.

Example: 23 27=? Solution:

2＋1＝3，2×3＝6，3×7＝21，23×27=621。Note: Multiply the single digits, and use 0 to occupy the place if the two digits are not enough.

3. The first multiplier is complementary, and the other multiplier is the same. Formula: After adding 1 to a head, the head is multiplied by the head, and the tail is multiplied by the tail.

Example: 37 44=? Solution:

3+1=4,4 4=16,7 4=28,37 44=1628,Note: Multiply the single digits, and use 0 to occupy the place if the two digits are not enough.