A fist clenched in the right hand means 0, food index 1, medium index 2, nameless index 3 and small index 4. Take back four fingers, then stretch out the thumb for 5, then stretch out the food index 6, the middle index 7, the nameless index 8, the little finger number 9, 10, the left hand stretch out 1, and the right hand clench fist number 0.

Addition and subtraction, addition is backwards, subtraction is backwards.

For example: 2+3.

The right hand stretches out the index finger and middle finger, indicating 2. Adding 2 means counting from the ring finger to 1, extending the little index finger to 2, retracting the four fingers and extending the thumb to 5. The answer is 5.

If it exceeds 10, it is necessary to carry it, that is, the index finger of the left hand is extended to indicate ten.

Add the formula within 20 minutes.

1+ 1=2。

1+2=3、2+2=4。

1+3=4、2+3=5、3+3=6。

1+4=5、2+4=6、3+4=7、4+4=8。

1+5=6、2+5=7、3+5=8、4+5=9、5+5= 10。