Give you an intelligent math! The right hand is a unit and the left hand is ten. When the thumb is extended by the right hand, it is 1, the thumb and forefinger are 2, the thumb, forefinger and middle finger are 3 and 4 in turn, the five palms are 5, the thumb is 6 (that is, the traditional 4), and the thumb and forefinger are 7 (that is, the OK appearance), which is 8.9. 10 in turn. Make a fist with your right hand and thumb with your left hand. In turn, the thumb of the left hand is 1, the right hand is 12, 13...20, that is, the right hand makes a fist, and the left hand extends the thumb and forefinger. Proficiency is convenient! For example: 3+2 gestures (thumb, index finger and middle finger) +2 sequentially open the ring finger plus 1, and open the little finger plus 1 is 5, for example: 4+4 gestures (thumb, index finger, middle finger and ring finger) +4 sequentially open the little finger plus 1.