All formulas for swallowing gold in sleeves

1 and 20 times the internal number.

Two numbers are multiplied within 20. Enlarge the sum of one digit of one multiplier and another multiplier by 10 times, and then add the products of the two multipliers.

Example:1:15x14 = 210, (15+4) x10+5x4 = 210.

Example 2: 15× 16 = 240, (15+6 )× 10+5× 6 = 240.

2. Multiplication of numbers with the same mantissa to swallow gold.

When two two-digit numbers are multiplied, the ten digits are the same and the single digits add up to 10, which is called the same mantissa. When you encounter this multiplication of numbers, multiply the ten digits by a number larger than it by 1, and then add the products of the two digits.

Example: 1: 23× 27 = 62 1, 20× 30+3× 7 = 600+21= 621.

Example 2: 25× 25 = 625, 20x30+5× 5 = 600+25 = 625.

Third, the method of multiplying the same number with the same head and tail to swallow gold

Multiply two digits, and the ten digits add up to 10, and the digits with the same digits are the same. This kind of number multiplication, first multiply the product of ten digits, then add one digit, then multiply by 100, and then add the product of single digits.

Example: 1: 23× 83 = 1909, (2× 8+3 )×100+3× 3 =1909.

Example 2: 35x75 = 2625, (3x7+5)x 100+5x5=2625.

I learned it when I was a child, and I calculate very fast. I am not familiar with it when I grow up. The more you use this thing, the faster it will be. When you are proficient, come out and forget it.