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There is not enough time for math in the senior high school entrance examination.
You can learn to calculate quickly, which will improve the speed of doing problems. When the test paper is handed out, you can read the big questions at the back first and then do a quick calculation of multiple-choice questions, such as 1. Ten times ten:

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.

This law can be deduced by algebraic method.

( 10+a)( 10+b)= 100+ 10(a+b)+ab

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.

Algebraic derivation of this law

( 10a+b)( 10a+c)= 100 aa+ 10a(b+c)+BC = 10a+ 10a 10+BC = 100 a(a+ 1)+BC

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.