Overview: 4 questions will be solved this time.Among them
           ☆4 integer calculations

[1/4 Integer column vertical calculation]
    Question type: Integer addition
    Original question: 12+9
    Solution:
    12+9 = 21
    Column vertical calculation:

			1	2
➕			1	9
			2	1

[2/4 Integer column vertical calculation]
    Question type: Integer subtraction
    Original question: 12-9
    Solution:
    12-9 = 3
    Column vertical calculation:

			1
			1	2
➖				9
			0	3

[3/4 Integer column vertical calculation]
    Question type: Integer multiplication
    Original question: 12*9
    Solution:
    12*9 = 108
    Column vertical calculation:

						1	2
✖							9
					1	0	8
					1	0	8

[4/4 Integer column vertical calculation]
    Question type: Integer division
    Original question: 12/9
    Solution:
    12/9 = 1 ··· ··· 3
    Column vertical calculation:

			1
9	丿	1	2
			9
			3

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