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

For example: 12× 14=?

Solution: 1× 1= 1.

,2+4=6

, 2×4=8

, 12× 14= 168

Note: Numbers are multiplied. If two digits are not enough, use 0 to occupy the space.

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.

For example: 23×27=?

Solution: 2+ 1 = 3

, 2×3=6

, 3×7=2 1

, 23×27=62 1

Note: Numbers are multiplied. If two digits are not enough, use 0 to occupy the space.

3. The first multiplier is complementary and the other 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.

For example: 37×44=?

Solution: 3+ 1=4

,? 4×4= 16

,7×4=28

, 37×44= 1628

Note: Numbers are multiplied. If two digits are not enough, use 0 to occupy the space.

4. Eleven times eleven:

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

For example: 2 1×4 1=?

Answer: 2×4=8

, 2+4=6

, 1× 1= 1

,? 2 1×4 1=86 1

, 5. 1 1 times any number:

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

For example: 1 1×23 125=?

Answer: 2+3=5

,3+ 1=4

, 1+2=3

,? 2+5=7

, 2 and 5 are at the beginning and end respectively.

1 1×23 125=254375

Note: If you add up to ten, you will get one.

6. Multiply a dozen by 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.

For example: 13×326=?

Solution: 13 bit is 3.

,3×3+2= 1 1

,? 3×2+6= 12

,3×6= 18

, 13×326=4238

Note: If you add up to ten, you will get one.