1, addition mental arithmetic: integer splitting and addition; For example; 8+5 = 13, first split "5" into "2" and "3"; Then it is 8+2+3 = 10. If you change an integer, subtract: for example, 26+ 18 = 44, and replace "18" with "20-2", then it is 26+20-2 = 44. Dislocation number addition: digit plus ten digits is one digit, 51+15 = 66; This is calculated as follows: 5+ 1 6; 1+5 gets 6; Put it together in groups of six.

2. Subtractive mental arithmetic subtracts integers and adds integers; For example; 52-7 = 45, as follows: change "7" to "10-3"; Then 52- 10+3 = 45. Dislocation number subtraction; The difference between ten digits and single digits is multiplied by 9. Multi-digit continuous subtraction; 387-50-42-3 1=264; It is easy to calculate first, 387-50 = 337, and then 42 plus 3 1 gets 73; Then, 337-73 can become 337-80+7 = 264.

3, more than ten times more than ten times, the formula is head-to-head, tail-to-tail, head-to-head, complementary tails, and the tails add up to 10, the formula, after adding 1 to a head, head-to-head, tail-to-tail. The first multiplier is complementary and the other multiplier has the same number. After a head is added with 1, the head is multiplied by the head and the tail is multiplied by the tail.

4, dozens of eleven times dozens of eleven, the formula is multiplied by the head, the head is added, the tail is multiplied by any number, the formula falls at the beginning and end, the middle and the drop-down, the second multiplier of the formula does not drop, the unit of the first factor is multiplied by each number behind the second factor, plus the next number, and then falls.

5. Rounding method in addition and subtraction, looking for the mixed operation calculation method of complement method. In the formula without brackets, only addition and subtraction or multiplication and division can be performed, from left to right. For the formula without brackets, multiply, divide, add and subtract first, and then add and subtract. If there are brackets in the formula, count the brackets first.