1, and the unit number is "1". Quick formula: the head is multiplied by the head, the head is added with the head, and the tail is 1 (rounded if the head is added with the head).

2, a dozen dozen. Quick formula: the head is 1, the tail is added, and the tail is multiplied by the tail (more than 10, carry)!

3. The same head and complementary tails (the mantissas add up to 10). Quick formula: add 1 to the head joint, and the tail-to-tail accounts for 2 digits!

The heads are complementary and the tails are the same. Quick formula: head multiplied by head plus tail, tail multiplied by tail 2 digits!

5. Multiply 1 1 by any number. Quick formula: the beginning and the end are fixed, and the two ends are added!

Algorithm:

1, integer addition calculation rule. The same numbers are aligned from the low order. When the numbers add up to ten, they will advance to the previous number.

2, integer subtraction calculation rules. The same numbers are aligned from the lower number. If the number of digits is not reduced enough, the number of digits from the last digit is reduced by ten, and then it is combined with the number of digits in the radix and then reduced.

3, integer multiplication operation rules. First, multiply the number on each bit of one factor by the number on each bit of another factor, then multiply the number on which bit of the factor, align the end of the multiplied number with which bit, and then add the multiplied numbers.

Operation introduction:

Mathematically, operation is a behavior, and a new quantity is obtained through possible combinations of known quantities. The essence of operation is the mapping between sets. Generally speaking, operation refers to algebraic operation, which is the correspondence in a set. For a pair of elements A and B taken out in sequence in set A, there is a unique third element C corresponding to it in set A, which is called the operation defined in set A..

From this operation, we can get two operations, that is, one of A and B is expected and C is known. The operation thus obtained is called the inverse operation of the original operation. For example, addition is the operation of finding a+b=c when A and B are known, then the operation of finding B when A and C are known, or the operation of finding A when B and C are known, is the inverse operation of addition, which is called subtraction.