For example: 13* 12
Methods: Hundred digits are 1, and ten digits are the sum of two digits.
A unit is the product of two digits.
that is
Hundred digits 1
Ten and five.
six
There are more than ten places, just move forward a few times when there are dozens.
For example, 14* 19.
The percentile is 1.
The decimal number is 13.
Enter the hundred digits of 1.
The unit is 36
Just enter 3 in ten positions.
The number is 266.
What's ninety times nine?
For example: 92*97
Methods: Take the sum of the difference between one number and another number 100 as the first two digits of the number. Multiply 10 by the difference of two-digit subtraction to get the last two digits of the number. If it is less than two digits, use zero to make up.
2-( 100-97)=89 ( 10-2)*( 10-7)=24
So the number is 8924.
(3) Fifty times fifty
For example: 58*56
Methods: First, use the product of 5*5 as the first two digits of the number, and use the product of 6*8 as the last two digits of the number, that is, 2548.
Next, divide the sum of 8+6 by 2.
Multiply by 100 and add the original 2548.
De 3248
If you meet 55 * 56, 5 and 6,
What should I do if the sum of 1 is divided by 2?
The business is the same as before. Another number plus 50.
That's it.
(4) Two digits are multiplied by the same ten digits and the complement.
Example 34*36
Method: multiply its ten digits by a number greater than ten digits as the first two digits, and use the product multiplied by one digit as the last two digits of the product.
That is 34 * 36 = (3 * 4) *100+4 * 6 =1224.
For example, 58*52=30 16
(5) Ten digits are complementary, and two identical digits are multiplied.
Example 37x77
Method: Multiply by ten digits and add the sum of two digits as the first two digits of the product.
Use the square of the unit as the last two digits of the product.
That is 37x77 = (3x7+7) x100+7x7 = 2849.
For example, 68x48=3264
(6) One digit is complementary to ten digits and multiplied by an iteration number.
For example, 37x99
Methods Ten digits plus 1 multiplied by iteration are the first two digits of the product, and the product of single digits multiplied by iteration is the last two digits.
That is 37x99 = (3+1) x9x100+7x9 = 3663.
Such as 46x77=3542
(7) Several eleven times several eleven.
For example: 3 1x5 1
Methods: The first two digits or the first digit of a number are multiplied by ten digits. The number of digits of the number is 1. Ten digits is the sum of ten digits of two factors.
That is 31x 51= 3x5x100+(3+5) x10+1=1581.
Such as 61x81= 4941.
(8) The difference of ten digits is 1, and the single digits are complementary.
For example, 37x43
Method: Take a large number and subtract the square of its single digit from the square of its ten digits.
Such as 37x43 = 40x40-7x7 =1551.
89x7 1=63 19
(9) Two digits multiplied by 99
For example, 38x99
Method Write the answer directly. The first two digits are two digits minus 1, and the two digits are the complement of two digits, that is, 3762.
This method also applies to the formula of multiplying several numbers by several 9.
The difference between these two numbers is 2.
For example, 49x5 1
Method Take the square of the average of these two numbers and subtract 1.
That is 49x51= 50x50-1= 2499.
(11) Ordinary two-digit multiplication
Example: 37x64
Take the product of ten digits as the front product and the product of single digits as the back product. Then add ten times the sum of the products of the inner term and the outer term.
That is 37x64 =1828+(3x4+7x6) x10 = 2368.
Paving algorithm:
37x64