1, and the number with the unit number "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 heads are the same and the tails are complementary (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, so are the tails.

Quick formula: head multiplied by head plus tail, tail multiplied by tail 2 digits!

5, 1 1 times 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. Calculation rules of integer subtraction

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. Calculation rules of integer multiplication

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.