Add:
Separate the units of these two addends from the ten digits, such as13+18 =10+3+10+8.
Then add these four numbers according to the difference between integer and decimal, such as10+3+10+8 =10+10+3+8.
At this point, it should be said that there is no problem in the process of total addition.
Then add, for example,10+10+3+8 = 20+11= 31.
Subtraction: (abdication)
Disassemble the minuend (≠ 100). This "disassembly" is necessary and must be decomposed into the sum of numbers with the tenth digit of 1, such as 63 = 50+ 13.
Decompose the subtrahend, such as 17 = 10+7.
Before teaching the following, we should emphasize that A-B-C = A-(B+C).
Primitive formula
=50+ 13-( 10+7)
= 50+ 13- 10-7 (emphasis on moving with numbers)
=50- 10+ 13-7
=40+6
=46
Subtraction: (minuend = 100)
With the skillful addition, you can break 100 into 99+ 1, and the problem will be solved.