1, ten times ten:

Formula: head joint, tail to tail, tail to tail.

2. The heads are the same and the tails are complementary (the sum of the tails is equal to 10)

Formula: After a head is added with 1, the head is multiplied by the head and the tail is multiplied by the tail.

3. The first multiplier is complementary

Another multiplier has the same number.

Formula: After a head is added with 1, the head is multiplied by the head and the tail is multiplied by the tail.

4, dozens of eleven times dozens of eleven.

Formula: head joint, head joint, tail to tail.

5, 1 1 times any number.

Formula: head and tail do not move down, middle and pull down.

6, more than ten times any number.

Formula: The first digit of the second multiplier does not drop, the single digit of the first factor multiplies each digit after the second factor, and then drops.

Extended data:

Methods to improve the speed of mental arithmetic;

1, imagine the formula. When you imagine numbers and formulas in your mind and solve the problematic parts, the new numbers you are dealing with will come to mind. Repeating numbers in your head and mouth in a low voice helps you remember the more important numbers in the formula. ?

2. Addition and subtraction. Mental arithmetic is best calculated from left to right.

3. The technical method of zero parity. If you want to calculate 200+400, you can remove the parity zero, and the formula becomes 2+4=6, and then add zero, and you can get the answer is 600.

4. Simplify the formula. If you want to calculate 30x60, you can simplify it to 3x6= 18, and then add zero to get 1800. You can simplify the formula by adding zero after the number.

5. Add and circle. When the sum exceeds 100, you can round it up first and then subtract the added number. Round 554 up to 560, and the formula becomes 560+207=767. Then subtract 6 from the sum 767 to get 76 1.

6. Calculate the multiplication. For example, when calculating multiplication 13x24, you can simplify some numbers and make mental arithmetic easier. Change 13 to 10, and the formula becomes 10x24 equals 240.

7. Calculation of mantissa. Then calculate the mantissa that has not been calculated just now, that is, 3 times 24 equals 72. Finally, 240+72 gives 3 12. This will make the calculation faster.

Baidu encyclopedia-mental arithmetic