What are the quick calculation skills of ape tutor?

Quick formula: head by head, head by head, tail is 1, head plus head exceeds 10, carry.

2. The decimal number is 1.

Quick formula: head 1, tail, tail. If it exceeds 10, carry it.

3. All single digits are 9.

Quick formula: each person adds 1, multiplies 10, and subtracts the added number, and finally subtracts 1.

Extended data:

Fast addition: the calculation method of fast addition of arbitrary digits is very simple. As long as learners remember a general formula of fast addition-"standard addition (decimal number) minus complement, and the previous digit plus 1", they can completely solve the problem of fast addition of any digit from high to low.

Fast calculation of subtraction: the fast subtraction for calculating any number of digits is also a general formula for fast subtraction-"standard subtraction (borrowed digits) is added and subtracted, and the previous digit is subtracted by more than one", which can completely solve the problem of fast subtraction for any number of digits from high to low.