First of all, "rounding" first:

That is, work out what can be added to an integer first. This method has been learned since the first grade, which is an extension of the method of adding ten.

For example: 28+54+46 = 28+(54+46) = 28+100 =128.

Second, change the operation order:

In the mixed formula with only "+"and "-",the operation order can be changed, which is later called the commutative law. Now just let the children know that they can be interchanged. Teachers in this school should have said that it is widely used in the process of addition and subtraction calculation.

For example: 85-17+18 = 85+(18-17) = 85+1= 86.

Third, calculate the sum of arithmetic continuous numbers:

This method is widely used in Olympic mathematics, which will save a lot of calculation time. Because there is division in the middle, PEP's children may not understand the second half, so parents need to worry. Other versions can be applied directly, no problem. This method is extended to 100, and it is also feasible to 1000.