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~ the beauty of communication mathematics: 7 up and 8 down formula puzzles ~
It is not difficult to imagine that this formula should be 10 xxxxx 8/ABC = 7xxx8, that is, the first line: 70xx, the second line: divisor), that is, abc) 10xxxxx8, the third line: 99x, the fourth line: 10xx, and the fifth line: 99x. The single digit of quotient is greater than 7, because abc multiplies it to get xxx8. Because142 * 8 =1136 and 142*9= 1278, the single digit of the quotient is 9, and the hundredth digit is 7, because the fifth line is 9xx. So this formula is10040678/142 = 70709.

For convenience, the division formula is named from line 1 to line 7 and step 1 from top to bottom. First of all, it is obvious that this is a division formula without remainder. The unit of line 7 is 8, so the unit of line 6 and dividend (line 2) is also 8. Of the three digits, only part of the number "1" is still three digits after multiplying by 7. So dividing by 100 is 1 Step 2: four digits-three digits = two digits. In this case, the hundredth digit of three digits must be 9, and four digits can only start with 10, so the second line is 10xxxxx8, the third line is 9xx, and the fourth line is 10xx. The fifth line is 9xx (x stands for space). Step 3: The thousand and ten digits of the quotient (i.e. 1 line) are all 0. Because the "first three digits" in line 4 and the "first three digits" in line 6 are not enough to divide by the divisor, the next digit should be added. Step 4: From lines 2 to 4, the maximum value of 10xx-9xx = 10xx can only be 1009, so the first four digits in the second line are 100x, and the third line is 99Step5: 99X, and only 994 is a multiple of 7. Step 6: It becomes easier and easier, because 852= 142×6 and1136 =142× 8, so the fifth line must be 94, and the hundred digits of the quotient are 7. Step 7: The seventh line is four digits, so the unit of the quotient must be greater than. That is, 8 or 91136 =142× 8, 1278= 142×9. The unit number of the seventh line is 8, so the seventh line is 1278, and the sixth line is also 1278 (there is no eighth step: 1006-994 = 12, so the fourth line is 1006 and the dividend is paid out. So the divisible formula is: line 65438 +0 (quotient): line 2 of 70709. The dividend is 10040678 Line 3: 994 Line 4: 1006 Line 5: 994 Line 6: 1278 Line 7: 1278.

-Only 10xx-9xx and the first two digits of 0xx-8 are 87xxxxx)10xxxxx89xxxx10x9xxxx8xxx8-Only 7x 1 is a single digit-Only 100x-99x and the rest/

7x2

7x3 and 7x4