Multiply two digits, the first digit is 1.
From the unit:
1. Multiply two mantissas to get one bit. Pay attention to carrying.
2. Add the two mantissas to get ten. Pay attention to carrying.
Multiply two numbers to get one hundred.
For example: 18× 19 = 342: 8× 9 = 72, then enter 7,2 as bits;
8+9+7=24, and then enter 2,4 to make ten digits;
Hundred-yuan 1× 1+2=3.
12× 13= 156
2. Multiply the two digits with the last digit 1
From the unit:
1. Multiply two mantissas to get one bit. Must be 1.
Add up these two places, it is ten. Pay attention to carrying.
Multiply these two numbers to get hundreds and thousands.
For example: 41× 71= 291131× 21= 651.
3, the top ten and the last ten
From a high position:
1. Multiply the first number and add 1 to get the first two digits or the first digit.
2. Multiply the two mantissas to get the last two digits.
For example: 76× 74 = 5624: 7× (7+1) = 7× 8 = 56 as the first two digits;
6×4=24 as the last two digits.
24×26=624
4. The tail is the same as the first one.
From a high position:
1. Multiply the two initial numbers and add the mantissa to get the first two digits.
2. Multiply the two mantissas to get the last two digits.
For example, 67× 47 = 3149: 6× 4+7 = 24+7 = 31is the first two digits;
7×7=49 as the last two digits.
62×42=2604
5. Multiply two digits by 1 1.
From the unit:
1. Change the mantissa of this number a little.
2. Add the prefix and mantissa to get ten digits. Pay attention to possible carry.
The first digit of this number is added to one hundred.
Such as: 35×11= 385 97×11=1067.
6. Multiply two digits by 99.
Use the formula "minus 1 complement" directly.
For example: 53× 99 = 5247: 53- 1 = 52 as the first two digits;
The last two digits are 100-53=47.
97×99=9603
7. Multiply two digits with the first digit of 9.
From a high position:
1. Subtract the complement of the second number from the first number to get the first two digits.
2. Multiply the complements of two numbers to get the last two digits.
For example: 95× 97 = 92 15: 95-3 = 92 as the first two digits;
5×3= 15 as the last two digits.
97×99=9603
8. Multiply two digits by 25.
1 First remember:
25×4= 100,25×3=75,25×2=50。
If this two-digit number is a multiple of 4, it is a multiple of 4, and the result is several hundred.
For example, 28×25=700, because 28 is seven times that of 4.
3. If this two-digit number is not a multiple of 4, then divide it into the sum of two numbers and ask one of them to be a multiple of 4.
Then, it is simplified according to the law of multiplication and distribution.
For example, 27× 25 = (24+3 )× 25 = 24× 25+3× 25 = 675.
9. Multiply two digits by 75.
1, first remember: 75×4=300, 75×3=225, 75×2= 150.
If this two-digit number is a multiple of 4, then the formula is "divide by 4 and multiply by 300".
Such as:16× 75 =16÷ 4× 300 =1200, 84× 75 = 84÷ 4× 300 = 21× 300 = 6300.
3. If this two-digit number is not a multiple of 4, the method is the same as above. You can divide it by the sum of two numbers and simplify it.
For example,15× 75 = (12+3 )× 75 = 900+225 =1125.
10, two digits multiplied by 15.
Just memorize the formula "Add half when you meet, and then multiply it by 10".
For example: 34×15 = (34+34 ÷ 2 )×10 = (34+17 )×10 = 510.
23× 15=(23+23÷2)× 10=(23+ 1 1.5)× 10=345。
Let's see if the algorithm is clever. Each method embodies the thinking ability of synthesis, analysis, generalization and reasoning.