Stretch out your hands, palms up. The fingers of the left hand are numbered 1, 2, 3, 4, and 5 starting from the thumb; the fingers of the right hand are numbered 6, 7, 8, 9, and 10 starting from the little finger.
When "ji" is multiplied by 9, you can bend the numbered finger. There are still several fingers on the left side of this bent finger, and the accumulated ten digits are tens; and how many more fingers are on the right side? Finger, the single digit of the product is how many.
Extended information:
9's multiplication formula skills:
1. Find patterns and compare notes: such as five nine forty-five and six nine fifty-four , seventy-nine sixty-three and four-nine thirty-six and so on.
2. Use stories to remember: Tang Monk went through ninety-nine and eighty-one difficulties, Sun Wukong had eighty-nine and seventy-two transformations, while Zhu Bajie only had half of his magic power and had forty-nine and thirty-six transformations.
3. Use homophones to remember: uncle is eighty-one years old (nine-nine-eighty-one)
4. Observe the origins of the ones and tens: several times nine, ten The digit is the number minus 1, and the ones digit is the number in the nine minus tens digit, such as four, nine, and thirty-six.
5. The rule of groups. Let's observe the products of "9's multiplication formula". Except for "one nine equals nine", what are the relationships between the other products?
For example: two-nine-eight, 18, nine-nine, eighty-one, 81. The two-digit single digits and tens digits have exchanged positions. Can you find a few sets of such formulas?
Three nine twenty-seven, 27; Eighty-nine seventy-two, 72;
Four-nine thirty-six, 36; Seventy-nine sixty-three, 63;
Fifty-nine forty-five, 45; sixty-nine fifty-four, 54.