1, abdication reduction: the abdication point (mark) must be pointed out when calculating in writing; The number marked abdication on the calculation time scale should be subtracted from 1 before calculation.

2. Continuous subtraction: When calculating continuous subtraction with a pen, two vertical forms can be listed. It is equivalent to doing two subtractions, except that the minuend of the second column is the result of the previous subtraction (the difference of the previous subtraction is the minuend of the second subtraction).

3. Addition and subtraction: Do two questions. It is best to use two vertical forms, and pay attention to the result of the addend (addition) or subtraction (subtraction) of the second formula and the previous vertical form.