Solution of finger pinch injury

Hold out your hand, palms up. The fingers of the left hand are numbered 1, 2, 3, 4, 5 from the thumb. The right hand starts from the little finger and is numbered 6, 7, 8, 9, 10 in turn.

Multiply "a few" by 9 and you will bend your first finger. There are several fingers on the left side of this curved finger, and the ten digits of the product are dozens; There are several fingers on the right. What is the single digit of the product?

Extended data:

9 multiplication formula skills:

1, compare the laws: such as 594 15, 6954, 796 13 and 4936.

2. Tell the story: Tang Priest experienced eighty-one difficulties, the Monkey King changed in 8972, Pig Bajie had only half the mana, and changed in 4936.

3. Homonym: My uncle is 81 years old (998 1)

4. Observe the unit and the origin of the tenth place: multiply by nine, the tenth place is a few minus 1, and the unit is the number on the tenth place minus nine, such as 4936.

5. Rules for grouping. Let's observe the product of "multiplication formula of 9". What is the relationship between other products except "19 gets 9"?

For example: 298, 18, 998 1, 8 1, two digits and ten digits have been exchanged. Can you find several groups of such formulas?

3927, 27; 8972, 72;

4936, 36; 796 13, 63;

594 15, 45; 6954, 54.